Editing Slide rule (section)

==Comparison to electronic digital calculators==
[[File:IBM 150 Extra Engineers 1951.jpg|thumb|upright|December 1951 advertisement for the IBM 604 [[IBM CPC|Electronic Calculating Punch]] explicitly comparing electronic computers to engineers calculating with slide rules]]

Even during their heyday, slide rules never caught on with the general public.<ref>Stoll, Cliff. "When Slide Rules Ruled," ''Scientific American,'' May 2006, [http://sliderulemuseum.com/Ephemera/ScientificAmericanMay2006_SR_byCliffStoll.pdf pp. 80–87]. "The difficulty of learning to use slide rules discouraged their use among the [[hoi polloi]]. Yes, the occasional grocery store manager figured discounts on a slipstick, and this author once caught his high school English teacher calculating stats for trifecta horse-race winners on a slide rule during study hall. But slide rules never made it into daily life because you could not do simple addition and subtraction with them, not to mention the difficulty of keeping track of the decimal point. Slide rules remained tools for techies."</ref> Addition and subtraction are not well-supported operations on slide rules and doing a calculation on a slide rule tends to be slower than on a calculator.<ref>Watson, George H. [https://books.google.com/books?id=KIyAn_jTGUYC&q=slide+rule&pg=PA110 "Problem-based learning and the three C's of technology,"] ''The Power of Problem-Based Learning'', Barbara Duch, Susan Groh, Deborah Allen, eds., Stylus Publishing, LLC, 2001. "Numerical computations in freshman physics and chemistry were excruciating; however, this did not seem to be the case for those students fortunate enough to already own a calculator. I vividly recall that at the end of 1974, the students who were still using slide rules were given an additional 15 minutes on the final examination to compensate for the computational advantage afforded by the calculator, hardly adequate compensation in the opinions of the remaining slide rule practitioners."</ref> This led engineers to use mathematical equations that favored operations that were easy on a slide rule over more accurate but complex functions; these approximations could lead to inaccuracies and mistakes.<ref>Stoll, Cliff. "When Slide Rules Ruled," ''Scientific American,'' May 2006, [http://sliderulemuseum.com/Ephemera/ScientificAmericanMay2006_SR_byCliffStoll.pdf pp. 80–87]. "With computation moving literally at a hand's pace and the lack of precision a given, mathematicians worked to simplify complex problems. Because linear equations were friendlier to slide rules than more complex functions were, scientists struggled to linearize mathematical relations, often sweeping high-order or less significant terms under the computational carpet. So a car designer might calculate gas consumption by looking mainly at an engine's power, while ignoring how air friction varies with speed. Engineers developed shortcuts and rules of thumb. At their best, these measures led to time savings, insight and understanding. On the downside, these approximations could hide mistakes and lead to gross errors."</ref> On the other hand, the spatial, manual operation of slide rules cultivates in the user an intuition for numerical relationships and scale that people who have used only digital calculators often lack.<ref>Stoll, Cliff. "When Slide Rules Ruled", ''Scientific American'', May 2006, [http://sliderulemuseum.com/Ephemera/ScientificAmericanMay2006_SR_byCliffStoll.pdf pp. 80–87]. "One effect was that users felt close to the numbers, aware of rounding-off errors and systematic inaccuracies, unlike users of today's computer-design programs. Chat with an engineer from the 1950s, and you will most likely hear a lament for the days when calculation went hand-in-hand with deeper comprehension. Instead of plugging numbers into a computer program, an engineer would understand the fine points of loads and stresses, voltages and currents, angles and distances. Numeric answers, crafted by hand, meant problem solving through knowledge and analysis rather than sheer number crunching."</ref> A slide rule will also display all the terms of a calculation along with the result, thus eliminating uncertainty about what calculation was actually performed. It has thus been compared with [[reverse Polish notation]] (RPN) implemented in electronic calculators.<ref name="Williams_2023"/>

A slide rule requires the user to separately compute the [[order of magnitude]] of the answer to position the decimal point in the results. For example, 1.5&nbsp;× 30 (which equals 45) will show the same result as {{val|1500000}}&nbsp;× 0.03 (which equals {{val|45000}}). This separate calculation forces the user to keep track of magnitude in short-term memory (which is error-prone), keep notes (which is cumbersome) or reason about it in every step (which distracts from the other calculation requirements).

The typical [[arithmetic precision]] of a slide rule is about three [[significant digits]], compared to many digits on digital calculators. As order of magnitude gets the greatest prominence when using a slide rule, users are less likely to make errors of [[false precision]].

When performing a sequence of multiplications or divisions by the same number, the answer can often be determined by merely glancing at the slide rule without any manipulation. This can be especially useful when calculating percentages (e.g. for test scores) or when comparing prices (e.g. in dollars per kilogram). Multiple [[Tachymeter (watch)|speed-time-distance]] calculations can be performed hands-free at a glance with a slide rule. Other useful linear conversions such as pounds to kilograms can be easily marked on the rule and used directly in calculations.

Being entirely mechanical, a slide rule does not depend on [[grid (electricity)|grid electricity]] or batteries. Mechanical imprecision in slide rules that were poorly constructed or warped by heat or use will lead to errors.

Many sailors keep slide rules as backups for navigation in case of electric failure or battery depletion on long route segments. Slide rules are still commonly used in aviation, particularly for smaller planes. They are being replaced only by integrated, special purpose and expensive flight computers, and not general-purpose calculators. The [[E6B|E6-B]] circular slide rule used by pilots has been in continuous production and remains available in a variety of models. Some wrist watches designed for aviation use still feature slide rule scales to permit quick calculations. The Citizen Skyhawk AT and the Seiko Flightmaster SNA411 are two notable examples.<ref>{{cite web|url=http://www.citizenwatch.com/en-us/watches/watch-detail/?model=JY0000-53E#filters=0000-53E|title=Citizen Watch Company – Citizen Eco-Drive / US, Canada, UK, IrelandCitizen Watch<!-- Bot generated title -->|work=citizenwatch.com|access-date=2014-04-21|archive-url=https://web.archive.org/web/20140422232006/http://www.citizenwatch.com/en-us/watches/watch-detail/?model=JY0000-53E#filters=0000-53E|archive-date=2014-04-22|url-status=dead}}</ref>