An ultrasonic instrument control that moves an A-scan display left or right without changing the distance between indications is called?

• A. Sweep Speed Control
• B. Gain Control
• C. Range Control
• D. Delay or Zero Offset Control

Answer: (D)

In an A-scan, the horizontal axis is the time-of-flight axis, which corresponds to depth in the material. The delay or zero-offset control shifts the entire trace along that axis by changing the reference start time without altering the actual time differences between reflections. So you can move the display left or right to position features where you want them, but the spacing between indications (which reflects the actual distances to the reflectors) stays the same. This is useful for aligning the trace to a reference surface or for comparing signals without distorting their true spacing.

Other adjustments affect how the signal is displayed in different ways: gain changes amplitude, range alters how much depth is shown, and sweep speed changes how fast the trace is drawn. None of these move the entire trace along the time axis while keeping the spacing between reflections unchanged.