AND Ion BM [BM-20] Microbalance 22 g x 0.001 mg - 25 mm Ø w/ Internal Calibration and Static Eliminator. The A&D Weighing BM-20 Ion BM Series Microbalance, 22g x 0.001mg features auto response adjustment allows balance to auto or manually stabilize FAST, MID, SLOW depending on draft & vibration influences. The BM20 auto self-calibration will detect changes in ambient temperature and auto calibrate.