Calibration block

A method of calibrating a thickness probe/gauge comprising:

• a) using a calibration block having a measurement face and a recess extending inwardly of the block from a face opposite the measurement face, wherein at least part of the surface of the recess is inclined relative to the measurement face in all directions from a central region on the inclined surface of the recess, and wherein the measurement face comprises a reference feature, the location of which corresponds to a known point on the inclined surface of the recess,
• b) defining a coordinate system in the plane of the measurement face of the calibration block and extending perpendicularly into the calibration block, the coordinate system having an origin at the reference feature,
• c) noting the actual position of inclined surface of the recess in the coordinate system,
• d) placing the thickness probe over the reference feature at an undetermined offset from the origin of the coordinate system and setting the nominal position of the thickness probe to zero,
• e) measuring the thickness of the calibration block at a plurality of recorded positions remote from the reference feature,
• f) plotting the measured thickness values in the coordinate system,
• g) constructing a measured inclined surface of the recess within the coordinate system from the plotted thickness value, and
• h) comparing the measured position of the inclined surface of the recess to the actual position of the surface of the recess and generating a value representing the offset of the thickness probe relative to the defined coordinate system.