Farady cages do not violate reciprocity. The path loss through the shield is the same in both directions. Be thankful this is so, or you'd be cooking yourself along with that microwaved burrito.
This is good advice, to which I'll add a few more points.
LCD displays have slow response at low temperatures. Be sure any you use is rated for the cold environment you're dealing with. Standard (less expensive) ones aren't suitable for sub-freezing temperatures.
Avoid moving parts. Consider a flash-memory card instead of a hard drive for the cold room systems (check the temperature specs for the flash, as well). If there must be disks, put them on a server located in a more forgiving environment.
You may also need improved moisture resistance for connectors and cables, if not the entire system. Besides condensation and frost issues, the word "freezer" suggests "food storage", which means wash-downs. Be sure to understand the client's expectations for such mundane issues, as well as the technical aspects.
It's not O2, but there is oxidizing material in the battery. Chemical batteries use redox reactions to deliver electric current. All the material needed to start the thermal run-away are sealed inside the cell: reducer (fuel) on one electrode, oxidizer on the other. Cutting off outside oxygen won't stop the battery's thermal run-away, it will only prevent other material (such as the plastic laptop case) from burning too. Because the case material is a poor fuel (safety regulations such as CSA/EN/UL 60950 require "flame-retardant" enclosures), the battery is the main source of heat. This is like trying to extinguish a road flare, not a grease fire on the stove.
It's simple, sad, and unfortunately not unusual. Akio Morita suffered a stroke, stepped down as chairman, and died a few years later. The suits took over. Without its visionary founder, another proud and vibrant company sank into mediocrity.
If you must keep confidential information on the hard drive instead of removable media, assume it will be stolen or damaged. Don't become the next "Zillions of confidential records stolen!" headline on CNN.
- Encrypt the data on the hard drive with the strongest encryption you have access to.
- Back up everything essential to a CD/R, DVD/R, USB stick, etc. (preferrably more than one copy)
- Encrypt the backups, too!
- Wipe all hard drive slack areas clean.
- Don't label the computer bag with company names and logos, or anything other temptation. Use "steal me!" cases for soiled laundry, not valuables.
That same month [July], a Dell notebook in the cab of a pickup parked alongside Lake Mead in Nevada caught fire, igniting ammunition in the glove box and then the gas tanks. The truck exploded. "A few minutes later and we'd have been coming up out of the canyon when the notebook blew up," said Thomas Forqueran, owner of the laptop and truck. "Somebody is going to wind up getting killed."
Lithium-ion batteries won't tolerate high heat. Leaving them in a parked vehicle on a summer day in the Nevada desert can expose them to temperatures much over the 60C (140F) specified maximum during dischage. Those warnings are printed on the case for good reason!
The "fire" claim seems exaggerated, too. The paper under the adapter has soot on it, but it doesn't appear to be charred or burnt. You can still see the writing through the soot, which is unlikely when paper smolders or ignites. The only scorched part of the cable is the small damaged area at the end of the strain relief. The fire didn't spread down the cable; the insulation damage is limited to a very small area at the end of the strain relief. It appears that the cable insulation self-extinguished without actually igniting the paper, just like it's supposed to. The mechanical design of the strain relief might be improved (larger bend radius), but it's neither a unique design nor the worst one on the market. This appears to be more a durability and ruggedness question than a safety issue.
If the author believes that the power supply has ineffective current limiting or that it is a fire hazard, the complete circumstances should be reported to the Consumer Product Safety Commission and the test agency whose approval mark appears on the power supply. That's the way to resolve a suspected safety problem. Griping accomplishes nothing.
The article indicated that they're using the internal 380Vdc from the UPS batteries and distributing that. What they're doing is avoiding the conversion of 380Vdc to 120/208/240Vac, then converting that back to 380Vdc in the front end of the server's switch-mode power supply. Fewer conversions, lower losses, better efficiency. So far, so good.
The problem is in the details of safe DC power distribution. Circuit protection and switching is much harder for DC than for AC. AC voltages goes to zero every half cycle, quenching the arc between open contacts. DC voltage is continuous, so DC breakers, fuses, and switches employ large contact gaps, sand fill, arc streching devices, larger parts, etc. to break the arc and allow the device to survive doing so. 500V DC rated fuses are much more expensive than the small 250Vac 3AG or 5x20 mm fuses in your system's PSU; DC rated circuit breaker are more expensive yet. Getting a 380Vdc powered server room to pass code inspection requires extra care and expense, which increases the time before the power savings pay for the upgrade.
IMO there's a better return on investment for buying more energy efficient AC powered equipment. Start with an efficient product base before committing to a DC power redesign. For a 24/7 data center at $0.0901/kWhr US average commercial power rates, every extra watt in the server costs $0.79 annually for electricity alone, not including the extra cooling to remove that watt from the building.
" "It's a temporary fix," one former senior NSA official said."
All computer room updates are temporary! When you continually upgrade and expand your installation, you continually change your power, cooling, and wiring needs. Facilties engineering and plant upgrades are an ongoing project, not a one-time quick fix. It isn't glamorous, it often isn't pretty, but it is essential. If management waits for a crisis like this before acting, you can bet on three things: the correction will take too long, cost too much, and after the too-late, too-expensive quick-fix they'll ignore it, assuring that the same thing happens again.
Yes, you can use a mechanical valve. But that, too, deters only the casual thief. Organized theft rings know about the cutoff trick, it's been around a long time, you can buy a starter cutout from J. C. Whitney, similar tricks have been in movie scripts (Biff's car in Back to the Future). The valve will be somewhere you can get to it, and it's attached to the fuel line. Thieves know this. They will follow the fuel line, find the valve you added, and open it. Indeed, they probably watched you using it while waiting for you to go inside. Your secret cut-off is not a secret!
If the valve is locked, they can break the lock, or cut the line and bypass it with a hose, or tow the car away...the list has no end. My point is that alarms, kill switches, "The Club", etc. are effective only against unsophisticated thieves. The chop shops can and will get your car if they really want it.
You'll deter the joy-riders, but a serious thief would hardly care. This type of device is too well known and too often touted to be fool-proof. Extra fuel (or ignition) cut-outs are like hiding your house key in a hollow fake rock: professional thieves see them in the stores too, so they know just what to look for. Or they will have a hot-wire harness ready to bypass such security blankets. Or a tow truck and uniform jacket (all nice and official looking, so he can claim to be the repo man if your neighbors ask questions). If the chop-shop pros want your exact car, they'll get it. All the security systems can hope for is to make them choose another target, which doesn't work if your car is rare or has unique parts in high demand. That's one reason I drive a rusty old PoS: as the saying goes, it isn't worth stealing (nor the insurance deductible, for that matter).
"Unfortunately the oil industry owns the patent on NiMH and has already attempted to shut down Toyotas use of the battery tech."
Ovonics invented the technology and holds many key patents. They have a 50/50 joint venture with oil company Chevron/Texaco, but it's quite a stretch from that to claiming "the oil industry owns the patent". This is particularly true when NiMH cells have been sold since 1983, which means the earliest patents on NiMH technology have already expired. The joint venture looks more like Texaco exploring strategies for survival in the post-peak-oil era than an evil plot to kill the hybrid car.
And why is that? Because professional spammers test their messages against SpamAssassin, etc. to find ways around the defenses. They know you can't set your filter too tightly without rejcting legimate mail, and businesses don't want to bounce customer inquiries. So they know there are cracks in the shield, and use their own shield to find them. They may be scum, but they aren't stupid.
It's also a reasonable DC supply voltage for an inverter (variable-frequency, variable-voltage drive) generating 240Vrms AC. So the GP has made a reasonable estimate either way.
If the dealer refuses to sell spare parts for my 1985 car because it's "too old" and "obsolete", I can go to the NAPA store or the junk yard to find them. I can (and do) fix my own old car myself; it was designed for reasonably easy service in the most common cases, and no reasonable repair is impossible. I can take it to any independent mechanic in town, and they'll fix it sooner than I could get an appointment at the authorized dealer's service shop. They sell a factory service manual that shows how to fix every part on the car. It's meant to be fixed, anywhere, any time, by any competent mechanic.
Compare that to closed-source software. There's no aftermarket parts. The EULA forbids transferring perfectly good used parts to another system. There's no service manual. Only the factory can fix it, and only if they want to: you're totally at their mercy. And yes, it needs fixing: there are still "critical" security updates for Win 98SE, and there are known "important" issues that Microsoft no longer supplies updates for. It's not a comfortable situation when you're running critical legacy applications for your business!
As a parent who uses the K-12 curriculum in a virtual charter-school setting, I appreciate the potential of this program. COVA has state-licensed teachers on staff to review the students' progress and confer with the parents. There are fieldtrips. There is Art, Music, and Science in the curriculum. The Chicago program adds weekly in-person attendance to this formula. Parents must be dedicated and work with their children, or a wash out will soon follow in either program. If you think home-school means goofing off and getting by with token efforts and sloppy work, avoid these virtual charter schools!
Because this program is a charter school of a school district, the teachers' union sees it as a threat similar to brick-and-mortar charter schools. Every student in a charter school program, virtual or physical, means one less student in traditional public schools. Per-pupil funding follows the students, threatening the status quo favored by the incumbents.
"With the use of modern image processing techniques, it is hoped that the original high quality TV images can be restored for public viewing before the magnetic data tapes deteriorate beyond repair." Is it likely the originals are still in good condition? 37 years is a long time for archiving magnetic media. This also implies that there are no high-quality, first-generation backups: what utter negligence! Nixon's 18 minute gap should have been sufficient warning!
If review is allotted only 2-1/2 hours, either the review is ineffective or you're deceiving yourself about how much time they really take. TFA is disingenuous when it says reviews take up 2-1/2 hours; it talks about having multiple 2-1/2 hour reviews. Review cycles logically occur at each step of the design hierarchy. The total time involved is far higher than 2-1/2 hours, but it is time well spent if it is spent properly.
A proper review means giving the reviewers review time, not just dropping a pile of code in front of each attendee 30 minutes before the meeting. The reviewers need time to comprehend what's being presented, to look for logical inconsistencies, to ponder what the user may do that wasn't allowed for, to track down unintended interactions, to find the right questions to ask. A reasonable figure is two hours of prep time for reviewers, spent at least a day in advance (the subconsious mind of sleeping reviewer is a powerful tool). Then the review meeting can move faster, while also being more effective.
If reviewers must start cold, finding a missing delimiter is a best case scenario. More likely, the meeting will be spent handling superfluous questions that arise because the reviewers don't understand the items being reviewed.
The article talks about fixing bugs during the review. YIKES! Impromptu decision-making is a recipe for compounding errors, especially when under the gaze of upper management. Every problem a reviewer brings to the table should come with a thoughtful plan of attack. Wild-ass guesses inevitably cause new problems, further corrections, and additional schedule delays.
The competition rules require 15MPH minimum average for six laps of a 1.6 mile track, and 25 MPH maximum for any one lap. There are considerable penalties for being too slow or too fast. This is about the same pace as a road bike.
They would have to be careful about false positives, and it sounds as if they are. They observe the shape of the retro-reflector, checking for the characteristic rectangular shape of a camera CCD. The retina is somewhat reflective, which is why camera makers include "anti-red-eye" devices for the flash. The method the article describes wouldn't target the round retina because it doesn't have the shape of a camera sensor.
This system should be effective against casual attacks, but serious opponents will find ways to defeat it. I wouldn't rely on it for protecting high value business or government information, but it should deter video recording in the theater. What's important from the studios' point of view is that the attacker now needs a cirumvention device. Talk to a good lawyer about the DCMA before making or buying one of those!
..and they are a threat to governments because there is no way to apply the road fuel tax to them...
Taxation is easily handled by a number of methods.
Method #1: Every year at license renewal time, require a certificate of the odometer reading from a licensed inspector, just like the emissions test certificate you need for a gas-powered car. Based on last year's mileage, you pay your highway taxes. The obvious drawback is the sticker shock when you see the annual bill, instead of paying piecemeal.
Method #2: The state estimates how many miles your car possibly could be driven, given its range and assuming daily recharges. Tax accordingly.
Method #3: Tax the electricty used by stand-alone charge centers and home rechargers. That requires a smarter meter for the home, or a separate meter just for the recharger.
Method #4: Drop the gas tax and make every road a toll road. It would be political suicide, and requires ubiquitous automatic toll technology (or using increased numbers toll both attendants to curb unemployment).
Method #5: Choose to not charge highway taxes for electric cars as a way to encourage and subsidize their use. That is what most states and the federal gov't are doing.
Point well taken. With estimated oil reserves of 1.1E12 to 1.3E12 barrels, 0.14 tons per barrel, and 85% of petroleum mass being carbon: 0.13E12 to 0.15E12 tons of carbon in the world's proven petroleum reserves. Estimated coal reserves are about 1.0E12 tons, six or seven times higher. But if all present petroleum and natural gas use shifts to a energy-equivalent usage of coal, estimated coal reserves would last about 75 years (compared to 285 years at the current consumption rate). Even sooner, if you consider the inefficiency of making coal as portable as petroleum (gassification, hydrogen generation, "syn-fuel", etc.) So economic limits for coal will occur just a generation or so after the petroleum economy fades away.
The increase in atmospheric CO2 comes from burning fossil fuels. However the rate of fossil fuel use will eventually begin to decline as economically extractable reserves are depleted, if we haven't already reached that point. Peak oil theory doesn't say that fossil fuels will disappear over night, but rather that the market will tighten with less fuel available at a given price. Economics, that is inability to buy as much fossil fuel as we want, will limit long-term carbon emissions regardless of energy politics. The question is how much damage and pain we'll inflict on ourselves along the way.
Unfortunately details are lacking (such as capacitance, voltage rating, size, projected cost, etc.). It probably uses the same trick as an electrolytic capacitor, where a conductive liquid forms one "plate" and the fibrous material is the other. The deliberately rough surface gives much more active surface area than a smooth electrode. The surface of the foil in an aluminum capacitor is like an aluminum sponge of microscopic scale. Nanotubes take this technique to a more extreme level.
Even though the article mentions problems with bifocals, it ignores one thing that gives great relief to the "more experienced" among us: a proper pair of prescription glasses for computer work. Bifocals are the pits: you can't keep the whole screen in focus, you slouch back in the chair or twist your neck to see the screen through the little "reading" window, and you wonder why you have a stiff neck and stress headaches. Get a pair of full-frame, single-vision glasses with a prescription suitable for your screen-reading distance. It's best to have the anti-glare coating, too.
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Farady cages do not violate reciprocity. The path loss through the shield is the same in both directions. Be thankful this is so, or you'd be cooking yourself along with that microwaved burrito.
LCD displays have slow response at low temperatures. Be sure any you use is rated for the cold environment you're dealing with. Standard (less expensive) ones aren't suitable for sub-freezing temperatures.
Avoid moving parts. Consider a flash-memory card instead of a hard drive for the cold room systems (check the temperature specs for the flash, as well). If there must be disks, put them on a server located in a more forgiving environment.
You may also need improved moisture resistance for connectors and cables, if not the entire system. Besides condensation and frost issues, the word "freezer" suggests "food storage", which means wash-downs. Be sure to understand the client's expectations for such mundane issues, as well as the technical aspects.
It's not O2, but there is oxidizing material in the battery. Chemical batteries use redox reactions to deliver electric current. All the material needed to start the thermal run-away are sealed inside the cell: reducer (fuel) on one electrode, oxidizer on the other. Cutting off outside oxygen won't stop the battery's thermal run-away, it will only prevent other material (such as the plastic laptop case) from burning too. Because the case material is a poor fuel (safety regulations such as CSA/EN/UL 60950 require "flame-retardant" enclosures), the battery is the main source of heat. This is like trying to extinguish a road flare, not a grease fire on the stove.
It's simple, sad, and unfortunately not unusual. Akio Morita suffered a stroke, stepped down as chairman, and died a few years later. The suits took over. Without its visionary founder, another proud and vibrant company sank into mediocrity.
- Encrypt the data on the hard drive with the strongest encryption you have access to.
- Back up everything essential to a CD/R, DVD/R, USB stick, etc. (preferrably more than one copy)
- Encrypt the backups, too!
- Wipe all hard drive slack areas clean.
- Don't label the computer bag with company names and logos, or anything other temptation. Use "steal me!" cases for soiled laundry, not valuables.
Lithium-ion batteries won't tolerate high heat. Leaving them in a parked vehicle on a summer day in the Nevada desert can expose them to temperatures much over the 60C (140F) specified maximum during dischage. Those warnings are printed on the case for good reason!
If the author believes that the power supply has ineffective current limiting or that it is a fire hazard, the complete circumstances should be reported to the Consumer Product Safety Commission and the test agency whose approval mark appears on the power supply. That's the way to resolve a suspected safety problem. Griping accomplishes nothing.
The problem is in the details of safe DC power distribution. Circuit protection and switching is much harder for DC than for AC. AC voltages goes to zero every half cycle, quenching the arc between open contacts. DC voltage is continuous, so DC breakers, fuses, and switches employ large contact gaps, sand fill, arc streching devices, larger parts, etc. to break the arc and allow the device to survive doing so. 500V DC rated fuses are much more expensive than the small 250Vac 3AG or 5x20 mm fuses in your system's PSU; DC rated circuit breaker are more expensive yet. Getting a 380Vdc powered server room to pass code inspection requires extra care and expense, which increases the time before the power savings pay for the upgrade.
IMO there's a better return on investment for buying more energy efficient AC powered equipment. Start with an efficient product base before committing to a DC power redesign. For a 24/7 data center at $0.0901/kWhr US average commercial power rates, every extra watt in the server costs $0.79 annually for electricity alone, not including the extra cooling to remove that watt from the building.
All computer room updates are temporary! When you continually upgrade and expand your installation, you continually change your power, cooling, and wiring needs. Facilties engineering and plant upgrades are an ongoing project, not a one-time quick fix. It isn't glamorous, it often isn't pretty, but it is essential. If management waits for a crisis like this before acting, you can bet on three things: the correction will take too long, cost too much, and after the too-late, too-expensive quick-fix they'll ignore it, assuring that the same thing happens again.
If the valve is locked, they can break the lock, or cut the line and bypass it with a hose, or tow the car away...the list has no end. My point is that alarms, kill switches, "The Club", etc. are effective only against unsophisticated thieves. The chop shops can and will get your car if they really want it.
You'll deter the joy-riders, but a serious thief would hardly care. This type of device is too well known and too often touted to be fool-proof. Extra fuel (or ignition) cut-outs are like hiding your house key in a hollow fake rock: professional thieves see them in the stores too, so they know just what to look for. Or they will have a hot-wire harness ready to bypass such security blankets. Or a tow truck and uniform jacket (all nice and official looking, so he can claim to be the repo man if your neighbors ask questions). If the chop-shop pros want your exact car, they'll get it. All the security systems can hope for is to make them choose another target, which doesn't work if your car is rare or has unique parts in high demand. That's one reason I drive a rusty old PoS: as the saying goes, it isn't worth stealing (nor the insurance deductible, for that matter).
Ovonics invented the technology and holds many key patents. They have a 50/50 joint venture with oil company Chevron/Texaco, but it's quite a stretch from that to claiming "the oil industry owns the patent". This is particularly true when NiMH cells have been sold since 1983, which means the earliest patents on NiMH technology have already expired. The joint venture looks more like Texaco exploring strategies for survival in the post-peak-oil era than an evil plot to kill the hybrid car.
And why is that? Because professional spammers test their messages against SpamAssassin, etc. to find ways around the defenses. They know you can't set your filter too tightly without rejcting legimate mail, and businesses don't want to bounce customer inquiries. So they know there are cracks in the shield, and use their own shield to find them. They may be scum, but they aren't stupid.
It's also a reasonable DC supply voltage for an inverter (variable-frequency, variable-voltage drive) generating 240Vrms AC. So the GP has made a reasonable estimate either way.
Compare that to closed-source software. There's no aftermarket parts. The EULA forbids transferring perfectly good used parts to another system. There's no service manual. Only the factory can fix it, and only if they want to: you're totally at their mercy. And yes, it needs fixing: there are still "critical" security updates for Win 98SE, and there are known "important" issues that Microsoft no longer supplies updates for. It's not a comfortable situation when you're running critical legacy applications for your business!
Because this program is a charter school of a school district, the teachers' union sees it as a threat similar to brick-and-mortar charter schools. Every student in a charter school program, virtual or physical, means one less student in traditional public schools. Per-pupil funding follows the students, threatening the status quo favored by the incumbents.
"With the use of modern image processing techniques, it is hoped that the original high quality TV images can be restored for public viewing before the magnetic data tapes deteriorate beyond repair." Is it likely the originals are still in good condition? 37 years is a long time for archiving magnetic media. This also implies that there are no high-quality, first-generation backups: what utter negligence! Nixon's 18 minute gap should have been sufficient warning!
A proper review means giving the reviewers review time, not just dropping a pile of code in front of each attendee 30 minutes before the meeting. The reviewers need time to comprehend what's being presented, to look for logical inconsistencies, to ponder what the user may do that wasn't allowed for, to track down unintended interactions, to find the right questions to ask. A reasonable figure is two hours of prep time for reviewers, spent at least a day in advance (the subconsious mind of sleeping reviewer is a powerful tool). Then the review meeting can move faster, while also being more effective.
If reviewers must start cold, finding a missing delimiter is a best case scenario. More likely, the meeting will be spent handling superfluous questions that arise because the reviewers don't understand the items being reviewed.
The article talks about fixing bugs during the review. YIKES! Impromptu decision-making is a recipe for compounding errors, especially when under the gaze of upper management. Every problem a reviewer brings to the table should come with a thoughtful plan of attack. Wild-ass guesses inevitably cause new problems, further corrections, and additional schedule delays.
The competition rules require 15MPH minimum average for six laps of a 1.6 mile track, and 25 MPH maximum for any one lap. There are considerable penalties for being too slow or too fast. This is about the same pace as a road bike.
This system should be effective against casual attacks, but serious opponents will find ways to defeat it. I wouldn't rely on it for protecting high value business or government information, but it should deter video recording in the theater. What's important from the studios' point of view is that the attacker now needs a cirumvention device. Talk to a good lawyer about the DCMA before making or buying one of those!
Taxation is easily handled by a number of methods.
Method #1: Every year at license renewal time, require a certificate of the odometer reading from a licensed inspector, just like the emissions test certificate you need for a gas-powered car. Based on last year's mileage, you pay your highway taxes. The obvious drawback is the sticker shock when you see the annual bill, instead of paying piecemeal.
Method #2: The state estimates how many miles your car possibly could be driven, given its range and assuming daily recharges. Tax accordingly.
Method #3: Tax the electricty used by stand-alone charge centers and home rechargers. That requires a smarter meter for the home, or a separate meter just for the recharger.
Method #4: Drop the gas tax and make every road a toll road. It would be political suicide, and requires ubiquitous automatic toll technology (or using increased numbers toll both attendants to curb unemployment).
Method #5: Choose to not charge highway taxes for electric cars as a way to encourage and subsidize their use. That is what most states and the federal gov't are doing.
Point well taken. With estimated oil reserves of 1.1E12 to 1.3E12 barrels, 0.14 tons per barrel, and 85% of petroleum mass being carbon: 0.13E12 to 0.15E12 tons of carbon in the world's proven petroleum reserves. Estimated coal reserves are about 1.0E12 tons, six or seven times higher. But if all present petroleum and natural gas use shifts to a energy-equivalent usage of coal, estimated coal reserves would last about 75 years (compared to 285 years at the current consumption rate). Even sooner, if you consider the inefficiency of making coal as portable as petroleum (gassification, hydrogen generation, "syn-fuel", etc.) So economic limits for coal will occur just a generation or so after the petroleum economy fades away.
The increase in atmospheric CO2 comes from burning fossil fuels. However the rate of fossil fuel use will eventually begin to decline as economically extractable reserves are depleted, if we haven't already reached that point. Peak oil theory doesn't say that fossil fuels will disappear over night, but rather that the market will tighten with less fuel available at a given price. Economics, that is inability to buy as much fossil fuel as we want, will limit long-term carbon emissions regardless of energy politics. The question is how much damage and pain we'll inflict on ourselves along the way.
Unfortunately details are lacking (such as capacitance, voltage rating, size, projected cost, etc.). It probably uses the same trick as an electrolytic capacitor, where a conductive liquid forms one "plate" and the fibrous material is the other. The deliberately rough surface gives much more active surface area than a smooth electrode. The surface of the foil in an aluminum capacitor is like an aluminum sponge of microscopic scale. Nanotubes take this technique to a more extreme level.
Even though the article mentions problems with bifocals, it ignores one thing that gives great relief to the "more experienced" among us: a proper pair of prescription glasses for computer work. Bifocals are the pits: you can't keep the whole screen in focus, you slouch back in the chair or twist your neck to see the screen through the little "reading" window, and you wonder why you have a stiff neck and stress headaches. Get a pair of full-frame, single-vision glasses with a prescription suitable for your screen-reading distance. It's best to have the anti-glare coating, too.