To set a combination firm joint caliper with a rule, when the legs are in position for outside measurements, grasp the caliper with both hands, as shown in figure 3-17A, and adjust both legs to the approximate setting. By adjusting both legs, the shape of the tool will be approximately symmetrical. Thus it will maintain its balance and be easier to handle.
Check this approximate setting as shown in figure 3-17B. Sight squarely across the leg at the graduations on the rule to get the exact setting required.
If it is necessary to decrease or increase the setting, tap one leg of the caliper, as shown in figure 3-18. The arrow indicates the change in setting that will take place.
When the caliper is set for inside measurements, the same directions for adjusting the setting apply. Figure 3-19 shows how the end of the rule and one leg of the caliper are rested on the bench top so that they are exactly even with each other when the reading is taken.