What does a small box on an ECG measure?

What does a small box on an ECG measure?

• A. 5 mm
• B. 0.5 mm
• C. 1 mm
• D. 2 mm

Answer: (C)

On ECG paper, the tracing is drawn on a grid where each tiny square is 1 millimeter wide and tall. That means a small box measures 1 mm. Each small box also represents 0.04 seconds of time horizontally and 0.1 millivolts of voltage vertically, while a larger box (made of 5 by 5 small boxes) is 5 mm per side. So the correct idea is that a small box is 1 mm in size; the other numbers correspond to the size of larger boxes or different units, not the small box itself.

On ECG paper, the tracing is drawn on a grid where each tiny square is 1 millimeter wide and tall. That means a small box measures 1 mm. Each small box also represents 0.04 seconds of time horizontally and 0.1 millivolts of voltage vertically, while a larger box (made of 5 by 5 small boxes) is 5 mm per side. So the correct idea is that a small box is 1 mm in size; the other numbers correspond to the size of larger boxes or different units, not the small box itself.