A 10-inch slide rule as shown in Fig. 232 is sufficiently accurate for most work, and, as it costs only a few dollars, it should be a part of the equipment of everyone who is doing even the simplest form of statistical work, or who is periodically plotting curves involving ratios or percentages. By using a slide rule the percentage ratios of numbers can be determined almost instantly and with no mental effort. It can be confidently predicted that anyone who has miich multiplication or division to do in relation to curve-plotting and chartmaking will find the slide rule of such a great assistance that the rule would not be parted with under any circumstances if a new one could not be obtained.

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Fig. 232. A lo-inch Slide Rule

The slide rule is of great convenience in doing work involving multiplication or division- It is especially valuable for obtaining ratios or percentages in statistics for industria' work

Judgment must be used in the showing of figures in any chart or numerical presentation, so that the figures may not give an appearance of greater accuracy than their method of collection would warrant. Too many otherwise excellent reports contain figures which give the impression of great accuracy when in reality the figures may be only the crudest approximations. Except in financial statements, it is a safe rule to use ciphers whenever possible at the right of all numbers of great size. The use of the ciphers greatly simplifies the grasping of the figures by the reader, and, at the same time, it helps to avoid the impression of an accuracy which is not warranted by the methods of collecting the data.