Usually, a depth gage has a vernier on it. We can justify by using a fairly unreliable instrument, such as a vernier caliper, because it provides a wide range inexpensively. However, depth micrometers beat vernier depth gages in terms of centimeters per dollar and reliability per dollar. The important point we need to learn about vernier depth gages, as well as depth micrometers, is that they conform with Abbeâ€?s law.
Align the scriber with an edge of a part resting on the surface base. You should use an indicator with the height gage for height measurement, except when you measure horizontal lines on the part. You must use a magnifying glass to accurately align the edge of the scriber to the line. We commonly use the scribe for layout. Although it is used in similar applications, the offset scriber also can be used all the way down to the level of the surface plate.
With a depth gage attachment, we can convert the instrument to a depth gage with very large range, which allows us to measure relative height differences in inaccessible places.
The most widely used attachment today is the indicator holder. The indicator magnifies the movement of a probe so that the need for feel is minimized. For greatest reliability, you should not use the indicator for measuring. You should use it only for zero setting. You should then take the measurements from the vernier scale of the height gage after you have moved the slide arm up or down to return the indicator reading to zero. The indicator does not convert the instrument into a dial height gage.