In case the bottom surface is used, 0.150 must be deducted from the reading of the caliper.
It is a 26-inch caliper, and will caliper up to 34 inches diameter.
Then the legs are closed to remove the caliper, and are reset to the scribed line.
Then remove the caliper and measure the distance between the caliper points.
The method of adjusting a spring caliper is shown at Fig. ...