1. The method of [1] for adjusting the instrument to a material can give a relative error of measurement more than ±2% if there is an additional signal delay. 2. The referred and relative errors may be reduced by using a standard specimen as close as possible in size to the workpiece, which serves to eliminate most of the error arising from this source in multiple measurements. 3. If limits have been specified for the refered or relative errors and values are known for δt, ri, and the speed of ultrasound, we can define limits to rmeas within which the errors in measuring the distance due to signal delay are not more than the specified values. 4. The error of measurement due to signal delay may be eliminated if not less than two echo signals are displayed on the oscilloscope during the adjustment and during direct measurement; the instrument should thus be set up from the difference of the readings corresponding to the first and n-th echo signals. These conclusions apply also to instruments of DUK-66 type, which use the same method of adjustment as the UDM-3.