Precision Calipers and Dividers
These calipers are used to measure the external size of an object. The same observations and technique apply to this type of caliper, as for the above inside caliper. With some understanding of their limitation and usage these instruments can provide a high degree of accuracy and repeatability. They are especially useful when measuring over very large distances, consider if the calipers are used to measure a large diameter pipe.
Government Printing Office The Official Gazette of the United States Patent Office (Washington, DC: Government Printing Office, 1895)