A method of determining a diameter of a probe tip mounted via a probe shaft to an arm of a coordinate measuring machine, the arm being movable within a measurement volume of the coordinate measurement machine in each of an x-axis direction, a y-axis direction, and a z-axis direction, wherein the x-axis direction, the y-axis direction, and the z-axis direction are each orthogonal to one another, the probe shaft movable to different angular positions with respect to the arm, the method comprising: determining a first diameter measurement of the probe tip by performing a calibration routine using a calibration piece with the probe shaft positioned at a first angular position with respect to the arm, wherein at least at one contact point (46, 48, 50, 52) during the calibration routine for determining the first diameter measurement, the arm is positioned at a first x-axis position along the x-axis direction, a first y-axis position along the y-axis direction, and a first z-axis position along the z-axis direction; moving the probe shaft to a second angular position with respect to the arm, different from the first angular position; determining a second diameter measurement of the probe tip by performing the calibration routine using the calibration piece with the probe shaft positioned at the second angular position with respect to the arm, wherein during the calibration routine for determining the second diameter measurement at least at one contact point (46, 48, 50, 52) that corresponds to the at least one contact point during the calibration routine for determining the first diameter measurement, the arm is positioned at a second x-axis position along the x-axis direction, a second y-axis position along the y-axis direction, and a second z-axis position along the z-axis direction, at least two of the second x-axis position, the second y-axis position, and the second z-axis position being different from the first x-axis position, the first y-axis position, and the first z-axis position, respectively; and averaging the first diameter measurement and the second diameter measurement to determine the diameter of the probe tip. determining a first diameter measurement of the probe tip by performing a calibration routine using a calibration piece with the probe shaft positioned at a first angular position with respect to the arm, wherein at least at one contact point (46, 48, 50, 52) during the calibration routine for determining the first diameter measurement, the arm is positioned at a first x-axis position along the x-axis direction, a first y-axis position along the y-axis direction, and a first z-axis position along the z-axis direction; moving the probe shaft to a second angular position with respect to the arm, different from the first angular position; determining a second diameter measurement of the probe tip by performing the calibration routine using the calibration piece with the probe shaft positioned at the second angular position with respect to the arm, wherein during the calibration routine for determining the second diameter measurement at least at one contact point (46, 48, 50, 52) that corresponds to the at least one contact point during the calibration routine for determining the first diameter measurement, the arm is positioned at a second x-axis position along the x-axis direction, a second y-axis position along the y-axis direction, and a second z-axis position along the z-axis direction, at least two of the second x-axis position, the second y-axis position, and the second z-axis position being different from the first x-axis position, the first y-axis position, and the first z-axis position, respectively; and averaging the first diameter measurement and the second diameter measurement to determine the diameter of the probe tip.