Review on IGaging 100 D68 Caliper Attachment Calipers by Tim Ram

but actual performance is likely to be less accurate than using a caliper base. I have a 4" of the same brand and the way this product attaches to the slide body is just not as balanced as it should be to get good flush readings. If you put it slightly over the base of your slide protruding and then zeroing the depth scale on the reference surface you may get a repeatable reading as my readings with that would not be reliable enough for the measurements I took (in the machine shop) This makes balancing easier and gives more area to cover of holes and pockets, but regardless of the accuracy of your caliper, add +/- 0.003" if you use it (and adjust it properly).