Slide calipers are multifunctional measuring tools. While they do not have the extreme precision of micrometers, they are very accurate and has more range than single micrometers.The best digital and dial slide calipers, regardless of resolution, are accurate to within .001" or .03mm, every 6" or 150mm. The best vernier calipers are accurate to .0005" or 0.013mm per foot or 300mm.Slide calipers come in different styles - electronic calipers, mechanical dial calipers, vernier calipers and plain slide calipers.Because slide caliper measuring surfaces are not in line with the beam of the caliper, some care should be taken not to use too much measuring pressure. This will lessen the possibility of springing the jaws. We use approximately one-half pound (.2kg) of pressure to set up the tools. However, a specific pressure is not necessary - just use good judgment for a minimum measuring pressure.If it is desired to check or set the separate I.D. nibs on a caliper, a micrometer or a ring gage can be used. Individual "feel" is important when measuring an I.D. This is because the measuring surfaces are so thin that small pressure changes that are normal from person to person can affect the reading as much as .001" (0.03mm) or so.It is important to keep the sliding surfaces clean and lightly oiled.