Hi @DIVER,
It seems I misunderstood your initial post - I thought you were saying you were expecting to measure 1000mm and were instead receiving measurements of 60mm, but you’re actually saying you’re having an error of 60mm from the measurement values you expected.
That seems reasonable, assuming you’re testing in fresh water.
That’s correct - the sonar transmissions and receiving are from the front of the device, where the blue ring is.
Given the consistency of those result, either your pool has its strongest acoustic reflection a bit below the surface that you’re measuring, or there’s some kind of offset error in the sonar’s estimation algorithm. Assuming the latter, can you try controlling the sensor in manual mode, and lowering the gain? It’s possible the readings may be saturated.