The international 10-20 system revisited: cartesian and spherical co-ordinates.

Methods like dipole source localization require an exact specification of the co-ordinates of electrode positions. Different values for the co-ordinates of F3, F4, P3 and P4 are encountered in literature. This is due to the unexpected complexity of the calculations involved and aggravated by an inaccurate but widely used control procedure for the placement of these electrodes. We present a table of co-ordinates for the 10-20 system together with a method for determining the co-ordinates of mid-way positions within the 10-20 system. The consequence of using erroneous co-ordinates on the accuracy of dipole source localization is discussed.