How do you measure with a slide rule?

Answer 1

First, it's not a slide "ruler," as was stated in the original question. It's a slide rule. Second, you don't measure anything with a slide rule. It's not a measurement device; it's an obsolete calculating device. It was used to simplify multiplication and division. Correction to original answer: The answer above (and the classification as a math category question instead of a mechanical measurement question) is based upon ignorance of the nature of, or existence of the slide caliper ruler. A slide caliper is a measuring tool used in mechanical applications. The caliper (not rule) consists of a metal strip or bar about 6.5 inches ling and 1/2 inch wide. One end has an extension about 1.5 inches long at right angles to the main bar. The main bar is inscribed with a scale, in inches - generally in 16ths of an inch. Affixed to the bar is a slide, with a similar extension. This second extension comes into contact with the first at the zero point. In the slide is a window, which is inscribed with a scale which is at a ratio of 7/8 to the scale inscribed on the bar. When the slide ruler is used to measure the outside dimension of an object the two extensions are in contact with the object on opposite sides. The dimension is read in a window in the slide. In reading the scale, it is noted that one of the inscribed lines on the 7/8 scale window will be virtually in line with one of the lines on the bar. The measurement is read by taking the measure at the "zero" line on the bar, and adding a factor derived from the matching lines. (That procedure is not known to me, but involves reading the "vernier scale".) The answer to the question as originally asked would depend upon whether the word "ruler" was intended to denote the slide caliper measuring tool, or - as assumed in the original answer - the slide rule formerly used in mathematical calculations.

Answer 2

With great difficulty.