* Surface plates must be calibrated on a regular basis to ensure that chipping, warping or wear has not occurred * A common problem with surface plates are specific areas or a section that is frequently used by another tool (such as a height gauge) that will cause wear to a specific point resulting in an uneven surface and reduced overall accuracy to the plate * Tools and workpieces may also cause damage when dropped on the surface plate or when material chips have not been removed * This will result in erroneous measurements and can only be fixed by resurfacing the plate * Cast iron unlike granite has also very uniform optical properties, and unlike glass or ceramic material very small light penetration depth which makes it a favorable material for certain optical applications * These plates are precision ground to Gade "0" Worskshop Grade