My grandfather was a German immigrant that repaired turbine generators in-situ. I have inherited many of his tools. Among them was this measuring instrument. It's a little like an adjustable square. It has one screw adjustment that loosens to dlide along the long axis or tightens to lock in place. The second screw, at right angles to the first, extends and retracts a small tab (only a half, to an inch of movement) along the flat plate that perpendicular to the main axis.
Any idea what it is?
Any idea what it is?