In an A-scan presentation, the horizontal line formed by the uniform and repeated movement of the electron beam across the fluorescent screen is called:

• A. A square wave pattern
• B. A marker pattern
• C. A sweep line
• D. None of the above

Answer: (C)

In an A-scan display, depth is represented by the timing of echoes, and the electron beam is driven by a time-base that sweeps across the screen. The uniform, back-and-forth or continuous left-to-right motion of that beam creates a visible horizontal line as it scans the fluorescent screen. This moving line is known as the sweep line. It’s the mechanism that maps elapsed time to horizontal position, while the actual echo information appears as vertical spikes above the baseline. A square wave pattern would describe a repetitive on-off signal, and a marker pattern would be static indicators, not the scanning motion that produces the display.