A calibration method for a printing apparatus is disclosed. The printing apparatus has at least one ink pen and a carriage for scanning the ink pen across a printing region. The calibration method includes: (a) printing a test pattern across a print medium at a constant carriage velocity; (b) optically scanning the printed test pattern to obtain a sensor signal thereof; (c) setting the carriage velocity so that there are acceleration, deceleration and constant velocity printing regions; (d) printing the same test pattern; (e) optically scanning the subsequent test pattern to obtain a sensor signal thereof; (f) comparing the sensor signals of the two test patterns to determine ink dot placement errors; and (g) calibrating time-delay compensation values based on the dot placement errors.