Abstract: A device which is useable to determine whether a hole is straight (i.e., perpendicular) with respect to the planar surface of the workpiece in which the hole is formed. The device structually comprises a rotatable shaft member having a collar with a centrally-located bore in which is held a probe (i.e., a mandrel) that is to be inserted into the hole to be checked. The collar also has an off-set bore which holds a horizontally slidably movable plunger of the vertically reciprocating type. A dial indicator is operably connected to the plunger. To test the hole for perpendicularity, the probe is inserted in the hole; the collar is rotated completely around the hole, and, the plunger follows the surface around the hole. If there is no change in the dial indicator reading, the hole is straight. If there is a change in the dial indicator reading, the hole is not straight; and, the lowest reading is subtracted from the highest reading.