Always remember to keep calipers clean and lightly oiled, but do not overoil the joint of firm joint calipers or you may have difficulty in keeping them tight. Do not throw them around or use them for screwdrives or pay bars. Even a slight force may spring the legs of a caliper so that other measurements made with it are never accurate.Keep in mind that they are measuring instruments and must be used only for the purpose for which they are intended.