The accuracy of the measured length with a Pile Integrity Test (PIT) device depends on the wave velocity selected for the specific type of pile being tested, which represents the speed at which stress waves travel through the pile. Different piles have different wave velocities, and accuracy can be affected by various factors, such as soil conditions. Thus, it's crucial to use an appropriate wave velocity and account for uncertainties in the measurement. The accuracy of the measurement can be improved by performing multiple tests at different locations along the pile and using advanced signal processing techniques to analyze the data.

An engineer can determine the wave speed within an accuracy of 10% based on concrete strength, and if a pile with known length has a clear reflection from the toe, the wave velocity can be calculated with precision and being used in the rest of the piles.