An apparatus for measuring variations in the flatness of an Almen strip holding surface includes a gaging block having opposing parallel surfaces defining an aperture extending between said parallel surfaces and substantially conforming to the size of the holding surface. A plunger is mounted in a cross member which extends across the aperture and is moved along opposite sides thereof. A dial indicator responds to displacement of the aperture to permit detection of any variation in flatness as the plunger is moved over the holding surface and along and between the side and end edges thereof. Placement of the Almen strip holding screws is verified to be in tolerance by the gaging block in that the gaging block cannot be mounted on the holding surface if the distance between the openings is out of tolerance.