The use of sound speed values to determine changes in the elastic constants due to applied or residual stress requires that such measurements be of high precision and low bias. For that reason, special evaluation tests to determine a representative precision and bias for the specific technique, method, and equipment setup used are given.

Speed of sound is a measure that depends on the accurate measurements of length of path of travel and transit time or other related parameters such as frequency, etc. Both measurements are subject to certain interpretations and assumptions and are highly dependent on laboratory expertise. This practice provides a means of checking overall technique.

This practice shall be used when it is necessary to assess the systematic and random errors associated with a particular speed of sound measurement in a solid medium. It can be used to check both equipment performance and measurement technique for these errors. It can also be used to study inherent errors in a particular method. It can also be used to assess proposed corrections to sound speed measurements such as the phase corrections of Papadakis (3, 4).

The resultant precision and bias determined by the use of the described block represents a more ideal situation than the same measurement performed in practice, in the field. Thus, the error for the specific field measurement may be larger than indicated by this test. This test represents the best error condition for a given technique and practice.