Patent ID: 8219353

Claim:
A method of determining absolute diameter of an object on a rotary table, comprising: given an assembly having (i) a rotary table on a base, (ii) a support tower on the base and carrying a horizontal measurement arm, and (iii) a laser device configured to indicate change in orientation of the horizontal measurement arm with respect to a centerline of rotation of the rotary table, the laser device having a laser path aligned relative to the centerline of rotation of the rotary table; calibrating the horizontal measurement arm including determining (a) a measurement error of the horizontal measurement arm at a reference height, (b) a displacement factor b CAL of the support tower, and (c) a displacement factor α CAL of the laser path, such that the sum of α CAL and b CAL is a constant value; using the horizontal measurement arm, measuring a plurality of points around a circumference of a subject object on the rotary table with the horizontal measurement arm at a height equal to or greater than the reference height, including measuring temperature of the horizontal measurement arm for each measured point and determining a thermal expansion factor; for each measured point, determining a respective corrected point by applying the thermal expansion factor, the measurement error and a compensation factor to the measure point, the compensation factor being determined as a function of α CAL , b CAL and height of the horizontal measurement arm relative to the reference height; and using the determined corrected points, determining an absolute radius, and, effectively, absolute diameter, of the subject object.