Best way to test gauges???

Miller tools used to have a special tool/gage for this. I'm not sure if it is still available. I believe that is is much safer to use without damaging your gages. I believe that it could test max, half, and min. I used to have two of them, but lost them in a move.

If you look in an old service manual 68,69 etc, it should list the tool number and you can call Miller tools and ask if it is still available.