In ultrasonic testing, which control adjusts the horizontal baseline of the A-scan display?

• A. Time Base Control
• B. Range Control
• C. Gain Control
• D. Scale Control

Answer: (B)

In an A-scan, the horizontal axis represents time of flight (which relates to depth in the material). The horizontal baseline is effectively the depth window you’re displaying. The control that sets which portion of that time/depth is shown—i.e., the depth window or range—determines where that baseline sits on the screen. Adjusting the range moves the displayed window along the time axis, shifting the horizontal baseline left or right. The time base would change how quickly the trace moves across the screen (the scale of the horizontal axis), while gain changes vertical amplitude, and scale typically affects vertical sensitivity.