1. This is a very "ordinary" slide rule. No special scales: no special history: no interesting use of colour: no abstruse gauge points. In a sense, though, that is what makes this rule important. We know a lot about the French court at Versailles - we know relatively little about how the other 99.99% of the population lived. There is a danger that if we don't preserve the "ordinary" rules, future historians of science will only know about the Analons and 2/83Ns.