How are deviations in measurement caused by wheeling the instrument not parallel to the axis taken care of?
The measuring calliper is supported by a four wheeled carriage. The contour of the wheel tyres, the position of the wheels and their angle are all designed to ensure that the carriage tracks accurately across the roll barrel. A typical hot mill work roll might be 2000mm long with a diameter of about 700mm and the departure from a perfect cylinder is usually less than 0.200mm so it can be seen that the roll itself forms part of a very accurate guidance system for the measuring calliper. On a 700mm roll the measuring tips would need to deviate from being at opposite ends of a true diameter (longest chord) by 2mm or 2000 micron to give an error in the profile reading (variation in diameter) of 0.006mm or 6 micron. Errors due to the measurement plane not being perpendicular to the roll axis are of the same order of magnitude. Furthermore because one is looking for variation in diameter (as opposed to absolute diameter) then even if the measurement plane is not perfectly perpendicular, prov
