Know How To Use a Slide Rule?
high_rolla writes "How many of you have actually used a slide rule? The slide rule was a simple yet powerful and important tool for engineers and scientists before the days of calculators (let alone PCs). In fact, several people I know still prefer to use them. In the interest of preserving this icon we have created a virtual slide rule for you to play with." Wikipedia lists seven other online simulations.
but in reality, justifying precision more than 4 significant places is really difficult using proper scientific/engineering methods. For instance 4 decimal places in surveying takes you to an inch range even over a mile of distance with hand tools. Average slide rules can do 2-3 fancy ones can hit that last place.