Coating thickness measurements near edges have a tendency to indicate larger measurement values, i.e. the actual coating is smaller than the displayed value. This effect occurs when the distance of the measurement point from the edge is smaller than the diameter of the probe.

The different probe diameters are shown in the table below.

 

Probe / Instrument	Probe diameter
1.5mm-probe (FN1.5, F1.5, N1.5), Surfix®, Pocket Surfix®	5 mm/0.20"
90°-probe (FN1.5/90°)	6 mm/0.24"
3.5mm-probe (FN3.5, F3.5), Surfix® easy	10 mm/0.4"
10mm-probe (F10)	20 mm/0.8"

However, if a measurement is to be made distinctly nearer to the edge than the probe diameter then calibration is to be carried out on an uncoated part exactly at the required distance to the edge. This calibration will then eliminate any edge error.