How to check the height Gage?

You should check height gages like you check vernier calipers—with the addition of checking the base-to–column squareness. Base-to–column squareness must be checked from a surface plate, so surface plate errors must also be checked. Therefore, height gage inspection and calibration should be done by the gage inspection department.
You can perform several tests on your own, however, that show whether the instrument needs to be calibrated. Regular visual inspection can reveal burrs, which can be removed, and nicks that may indicate sever abuse or damage. In addition, the base should not rock on a flat surface, which you can determine by applying pressure at various places. A truly flat base will “wring�?to a fine surface plate and you will feel drag or suction when you slide the instrument.
The best way to test accuracy and precision is to make repeated readings of gage block height at various points throughout the range. Again, it is not enough to repeat the measurements. If , after you have corrected the zero setting by adjusting the vernier plate, the precision (dispersion of repeated readings) or the accuracy (repeating readings of the gage block height ) is more than the discrimination of the instrument (20Чm /0.001 in.), you should return the instrument to the manufacture for repair. You should always inspect your accessories as carefully as you inspect the instrument itself.