Using a comparison or stereomicroscope, land and groove impressions can be measured using a variety of equipment:
- Glass measuring reticule
- Electronic reticule
- Digital measuring equipment and software
- MP 6 optical projector (no microscope)
- Machinist’s scale
Descriptions of each of the above equipment can be found in Module 7.
A technique used by many examiners for measuring the widths of land and groove impressions is the air gap method. This technique is fast and accurate, requiring only a calibrated microscope and a micrometer. Calipers can be substituted for the micrometer.