The probability of having a TV estimation error less than X ml as a function of X, for the body surface and intracardiac leads, using the instantaneous percent modulation measurement, at TV 0 ml (A), 250 ml (B), 500 ml (C), and 750 ml (D). An arbitrary point (x, y) in these plots reflects that the probability of having an estimation error of less than x ml is equal to y.