Editing Slide rule (section)

===Standard linear rules===
[[File:Teaching sliderule comparison.jpg|thumb|A normal-sized slide rule sitting inside a {{convert|7|ft|m|adj=on}} teaching model]]

The width of the slide rule is quoted in terms of the nominal width of the scales. Scales on the most common "10-inch" models are actually 25&nbsp;cm, as they were made to metric standards, though some rules offer slightly extended scales to simplify manipulation when a result overflows. Pocket rules are typically 5&nbsp;inches (12&nbsp;cm). Models a couple of metres (yards) wide were made to be hung in classrooms for teaching purposes.<ref>{{cite web |url=http://www.tbullock.com/sliderule.html |title=Slide Rules |publisher=Tbullock.com |date=2009-12-08 |access-date=2010-02-20 |archive-url=https://archive.today/20130203202414/http://www.tbullock.com/sliderule.html |archive-date=2013-02-03 |url-status=dead }}</ref>

Typically the divisions mark a scale to a precision of two [[significant figures]], and the user estimates the third figure. Some high-end slide rules have magnifier cursors that make the markings easier to see. Such cursors can effectively double the accuracy of readings, permitting a 10-inch slide rule to serve as well as a 20-inch model.

Various other conveniences have been developed. Trigonometric scales are sometimes dual-labeled, in black and red, with complementary angles, the so-called "Darmstadt" style. Duplex slide rules often duplicate some of the scales on the back. Scales are often "split" to get higher accuracy. For example, instead of reading from an A scale to a D scale to find a square root, it may be possible to read from a D scale to an R1 scale running from 1 to square root of 10 or to an R2 scale running from square root of 10 to 10, where having more subdivisions marked can result in being able to read an answer with one more significant digit.