Abstract: A datuming device is provided for use with a machine tool having a movable member which is guided under computer numerical control. The datuming device permits measurement of displacements in a direction not parallel with a displacement probe's line of travel. The device includes a non-sensitive surface which, when probed by the displacement probe, does not indicate a changing displacement when the movable member is moved from a first position to a second position. The nonsensitive surface serves as a reference surface. The device further includes a sensitive surface which, when probed by the displacement probe, exhibits a changing displacement when the movable member is moved from the first position to the second position. The sensitive surface is generally configured as an inclined surface on the datuming device.