Chapter One - What is a Slide Rule? 1What is a Slide Rule?Definition of a Slide Rule ... and What It Can and Can’t DoA slide rule is a simple looking mechanical device based on logarithms thatperforms a wide range of mathematical operations. Visually, it just looks like anassembly of sliding and stationary scales, but hidden in the design of the scalesis extraordinary mathematical sophistication, able to perform simple operationsfrom multiplication or division to complicated fractional powers and roots, andcomplex trigonometric functions. The range of its power is quite incredible, andfew people can even perform its more complex functions manually. For example,how are your manual cube root skills today?It can work with numbers of any size but can typically provide only 3 significantfigures of resolution. It also does not do regular addition and subtraction(get out your abacus for that), although its fundamental design is based on theaddition and subtraction of logarithmically related distances.Precision of 3 significant figures is enough for most engineering design inthe real world, as it provides accuracy to 0.1%, quite adequate for serious work,especially in a world where many measurements and parts are rarely even accurateto 1%. Your calculator may produce 8 significant figures, but when thetotal uncertainty of your data is considered, often only 3 are used.The slide rule also has one truly magical property – it is a parallel calculator,rather than a serial one like your desktop electronic calculator. Once arelationship is set up on a slide rule, all variations are also set up at the sametime, allowing you to have a visualization of changing results with differentvalues, without any additional real work. On your electronic calculator, you willbe pressing buttons for hours to see what a slide rule does just by existing. In theengineering world, this is called a “Monte Carlo” analysis, where the values arevaried to see the results, usually with a powerful computer to provide thecalculating horsepower. Even the lowliest student slide rule does thisautomatically.For a simple example, let’s say you are on vacation in India and want tobuy an antique statue. Set up the exchange rate of rupees to dollars or yourcurrency of choice on your slide rule, and you can see what it costs, BUT, youalso see every other price at that rate at the same time (thus making dickeringK&E 4O53-3F, 25 cmscales (“1O inch”), celluloidon mahogany core,simplex, USA. Front andedge view.
2All About Slide Rulesover the price much easier). This is quite amazing, and impossible for yourelectronic calculator, but just everyday life for a slide rule.Unique Characteristics of the Slide Rule• The slide rule demonstrates elegant simplicity (few pieces, only two movingparts).• It embodies classical grace (its dimensions approximate the ratio of length towidth of a column in a Greek temple such as the Parthenon).• It has total “transparency” (every register and scale is readily visible).• It has very large dynamic range and sufficient precision for most engineeringtasks.• It is easy to learn and simple to operate.• It provides automatic parallel computations.• And it has wide computational flexibility.These features, when coupled with the slide rule’s different scales andlabels, hint of great complexity and tactile, intimate control of mathematics.To appreciate the power of this deceptively simple looking tool, pick up awell-made example, and feel its weight, balance, and precision.You hold mathematical magic in your hands!The scales and arrangements have been refined through 20 generations ofmathematicians and engineers, creating adjacent mathematical relationshipsthat still outperform the calculator and computer generated spreadsheet forcertain problems in electronics, surveying, financial risk forecasting, and proportiondependent analysis.This is simply magic to the uninitiated ... and a marvel to watch in action.How Slide Rules are MadeThe most commonly seen slide rules are made of wood or bamboo coveredwith celluloid or are made entirely of plastic. One leading American companymade them of aluminum. Some were made of plain wood or steel or othermetals.Pickett N1010ES, 25cmscales, aluminum, USA
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