Reading The Gauge; Mm Gauge - HP 85091A Reference Manual

Reading the Gauge

Gauge increment refers to the distance of one minor division between
two adjacent minor divisions, or one-tenth of a major division (0.0001
inch). A gauge increment is the smallest value shown on the gauge face.
For each revolution of the large dial, the smaller dial indicates a change
of 0.01 inch. Use the small dial as the indicator of multiples of 0.01 inch
up to 0.25 inch. In most measuring applications, this value remains
zero.
If the needle has moved clockwise, the center conductor is protruding
and the value is determined by the black numbers.
If the needle has moved counterclockwise, the center conductor is
recessed by an amount determined by the red numbers.

7 mm Gauge

You must remove the collet with the collet extractor tool prior to
CAUTION
performing pin depth measurements.
Figure 3-6
While performing pin depth measurements, use different orientations
of the gauge with the connector. Average a minimum of three readings,
each taken after a quarter-turn rotation of the gauge, to reduce
measurement variations that result from the gauge or the connector
face not being exactly perpendicular to the center axis.
Chapter 3
Using a 7 mm Connector Gauge
Gauging and Making Connections
Gauging Techniques
3-23