Probably no part of the shop equipment is so often improperly selected as the pocket rules. These should be selected for accuracy, convenience, and to familiarize oneself with the rule which he is likely to use after leaving school. For this reason all two-foot, two-fold rules are unsuitable. Of the four-fold rules the number 84 is probably the best, price considered. In no case use the ten-cent style, or one having neither edge brass-bound.

Be very particular to use the rule exactly as directed. Many of the directions given may appear wrong or needless to those not familiar with practical work, but nevertheless every direction given is the result of much experiment and use. Whenever possible we should use the rulings away from the end, as shown in Fig. 17. The corners not only soon become incorrect from wear but very often the graduations at the extreme ends are not made correctly. The number 84 rule and also the number 62 rule (Fig. 177) have the inches divided into eighths, sixteenths, tenths, and twelfths. These are a very useful variety of graduations, and you should accustom yourself always to use the rule in the same manner and then there will arise no trouble from getting the various scales confused.

Hold the rule, opened to one foot long, in the right hand as shown in Figs 14 and 17, when using either eighths or sixteenths. The tenths and twelfths are on inside edges and therefore we never use them by mistake if the rule is held in this manner. When opened to two feet long, if we always hold the rule on edge, the center hinge up, we are sure to use only eighths or sixteenths. To use the tenths or twelfths we must place the rule in an uncommon position.

Fig. 177. Pocket Rule. The No. 84. Rule is the same as this one except that only the outside edges are brass bound.

The drafting scales marked one fourth, one half, etc., may be used to take the dimensions from scale drawings. The even inches are measured with the rule in the ordinary manner. The fractions of an inch are obtained by setting the compasses to the distance on the drawing and then applying them to the scale as in setting them, as shown in Fig. 99.

The proper method of using the rule in laying off given spaces is shown in Figs. 18, 123.