A method of measuring the maximum thickness of a mailpiece while it is moving through a mail-handling machine. The method includes: acquiring a thickness measurement; recording the measured value in a register; determining a maximum value and a minimum value of the register; determining a difference between said maximum value and minimum value, and comparing the difference with a predetermined threshold value; and if the difference is less than the threshold value, and if the maximum value is greater than a current maximum thickness value, taking the maximum value as the new current maximum thickness value for the mailpiece.