The distance from Fpz to T4 is 14 cm. What is the distance from Fpz to F8?

The distance from Fpz to T4 is 14 cm. What is the distance from Fpz to F8?

• A. 4cm
• B. 10cm
• C. 7cm
• D. 3cm

Answer: (C)

In the 10-20 system, distances between scalp electrode placements are treated as arc lengths along the head. Fpz sits at the midline of the forehead, while F8 is a lateral frontal position and T4 sits further back on the right temporal area. F8 lies roughly midway along the arc from Fpz to T4, so the distance from Fpz to F8 is about half of the distance from Fpz to T4. If that distance is 14 cm, half is 7 cm. So the best estimate for the distance from Fpz to F8 is 7 cm. Exact values vary by head size, but 7 cm is the most plausible given the options.

In the 10-20 system, distances between scalp electrode placements are treated as arc lengths along the head. Fpz sits at the midline of the forehead, while F8 is a lateral frontal position and T4 sits further back on the right temporal area. F8 lies roughly midway along the arc from Fpz to T4, so the distance from Fpz to F8 is about half of the distance from Fpz to T4. If that distance is 14 cm, half is 7 cm. So the best estimate for the distance from Fpz to F8 is 7 cm. Exact values vary by head size, but 7 cm is the most plausible given the options.