Ionizing radiation is used for different purposes in medical procedures, mainly diagnostic imaging, nuclear medicine, and radiotherapy. While using radiation to the medical applications, one need to ensure the radiation level must be within the permissible limit for patients as well as staff as prescribed by AERB. To measure the radiation level, Area survey meter is being used. Protection level area survey meters must be calibrated against a reference instrument that is traceable (directly or indirectly) to a national standards laboratory.