A-Line Manufacturings sag check is a test that determines the amount an indicator bracket will sag at a given distance.
How to perform a sag check
Clamp the brackets on a sturdy piece of pipe the same distance they will be when placed on the equipment. Zero both indicators on top, then rotate to the bottom. The difference between the top and bottom reading is the sag.
Sag will always have a negative value, so when allowing for sag on the vertical move always start the dial indicator with a plus(+) reading. For example if you have .002" sag; when you zero your indicators on top put the needle on a +2 instead of zero to compensate for the sag.