down the items on a piece of paper for addition later by mental effort. With the portable adding machine the data are taken from the original work directly and added automatically as the work proceeds.
Engineers do the greater portion of all of their computing work by means of the slide rule. By others than engineers, however, the slide rule is very little used. In the preparation of data for curves and charts for corporation work, or for any investigations where numerous percentages are necessary, the slide rule is almost indispensable. 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 much multiplication or division to do in relation to curve-plotting and chart-*making 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 10-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 industrial
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.
A recent government report[1] contained this statement: "The cotton crop of last year (1911) aggregated 16,250,276 500-pound
- ↑ "The Packing and Marketing of Cotton," by John M. Carson.
