Clamp meter est means accurate, safe and reliable. EST is a registered trademark of Huajinghui No. 42275928. It is approved for use on measuring instruments and other products. It is the abbreviation of the English letters Exacty, Safety and Trusty, which means accurate, safe and reliable measuring instruments. Clamp ammeter is referred to as clamp meter. Its working part mainly consists of an electromagnetic ammeter and a through-core current transformer. The core of the through-core current transformer is made into a movable opening and is in the shape of a clamp, hence the name clamp ammeter.