AND Ion BM [BM-252] Microbalance, 250g x 0.01mg - 90 mm Ø with Internal Calibration. The A&D Weighing BM-252 Ion BM Series Semi-micro Balance, 250g x 0.01mg 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.