How frequently should my liquid particle counter be calibrated?

Специалист по калибровке Beckman Coulter
Calibration services should be performed in accordance with ISO 11171/21501-3 requirements using NIST-traceable equipment and particle media. Beckman Coulter offers service continuity and peace of mind with 6-month, annual or customized service options, based on regulatory and GMP/cGMP guidelines.