![](https://cos-cdn.shuashuati.com/pipixue-web/2020-1231-2005-12/ti_inject-812ce.png)
Using the immersion method, a distance amplitude curve (DAC) fir a 3/4 inch diameter, 5MHz search unit shows the high point of the DAC at 1 1/2 inch block. One day later the high point of the DAC for the same search unit is at the 3/4 inch block. Assuming calibration has to changed, this would indicate that the search unit.