To assure accurate readings All AMES Hardness Testers, whether in constant use or not, require accuracy checks. To check accuracy, take several readings on the test block. The readings on the barrel dial should agree with the marking on the test block.   ASTM Standard E-18 (for testing Rockwell Hardness) says, in part:         So, always apply the penetrator to the same side of the test block, only on areas not marked by previous tests. When you cannot be certain of placing the penetrator on a perfectly unaffected part of the surface, you need a new test block. Ames offers a variety of traceable, certified blocks.   For accurate results, depend on Ames Certified Test Blocks Serialized and traceable to national standards. Available in all scales.        Once per year: your tester should be factory re-calibrated. Call for details or click the E-Mail button to send an e-mail.