If the distance from Fp2 to O2 is 30cm, what is the distance from C4 to P4?

To determine the distance from C4 to P4 given that the distance from Fp2 to O2 is 30 cm, it's essential to understand the general layout of the 10-20 system of electrode placement used in EEG.

The distance between electrodes on the same lateral axis can be proportional based on their placement. In the 10-20 system, the sections of the head from Fp to O, and subsequently from C to P, represent specific sections of the scalp that generally follow a consistent anatomical proportion based on average head measurements.

The distance from C4 to P4 is generally shorter than the distance from Fp2 to O2 due to their anatomical positioning and grouping within the 10-20 system. Specifically, the distance between C4 and P4 is approximately one-fourth of the distance from Fp2 to O2 because the C and P electrodes are placed more closely together compared to the frontal and occipital electrodes.

In this case, if the distance from Fp2 to O2 is 30 cm, we can derive that the distance from C4 to P4, being approximately one-fourth, is 7.5 cm. This proportionality in the 10-20 system underpins the