An optical-mechanical gauge such as the Paint Inspection Gauge, if set up correctly, will not be subject to appreciable calibration change except by gradual wear of cutters and guide studs.

On the other hand, “surface proximity gages”, magnetic, inductance, or eddy current types generally require calibration before any series of measurements; and frequently within a series of measurements - especially if the surfaces are variable in type and structural thickness. STANDARDS ARE A FUNDAMENTAL REQUIREMENT FOR RELIABLE THICKNESS MEASUREMENT.

Operating instructions for measuring instruments will normally include calibration procedures. In the absence of written procedures, the user is advised to contact the instrument manufacturer. In general, proximity type instruments are most reliably calibrated for a given measurement by selecting two standard films which “bracket” (one above, one below) the expected film thickness to be measured. By first causing the instrument to read both standards correctly over a bare surface (the same or similar to the coated one), then the unknown reading should be correctly made. Of course, the narrower the range between the two standards the lesser are the possibilities of errors due to instrumental non-linearities.

An optical-mechanical gauge may be calibrated by the owner following a simple verification procedure on a standard test panel. If observed thicknesses deviate from “true” values, a calibration curve can be drawn to specify necessary corrections. Restoration of “zero” correction, if desired, will usually require attention by the manufacturer’s shop to re-establish precise alignment.

The following types and grades of film thickness standards are supplied in sets: