MASTER-20PM is for low concentration measurements such as juices, cutting oil, etc. The MASTER-M / PM series is a good alternative choice when the water resistant feature is not a priority and the Temperature Compensation will be carried out manually. Not equipped with the Automatic Temperature Compensation feature.
The MASTER-20M is made of metal, and the MASTER-20PM is plastic. The specifications are exactly the same. For salty and acidic samples, choose the plastic body, MASTER-20PM.For the model with Automatic Temperature Compensation please choose
MASTER-20Pα. 
