Using letters different from A, B, C, and D ( the letters used for the capillary electrometer's waveform ) facilitated comparison when the uncorrected and corrected lines were drawn on the same graph . and these letters are still in use today.
12.
Einthoven had previously, in 1895, assigned the letters P, Q, R, S, and T to the deflections in the theoretical waveform he created using equations which corrected the actual waveform obtained by the capillary electrometer to compensate for the imprecision of that instrument.
