Milwaukee Calibrator Liquid Ph 4.01 20ml.

Calibrating liquid pH 4.01-20 ml. in Envelopes.
This pH 4 liquid is used to calibrate digital meters and keep them in perfect working order.
If you want to make exact measurements you will need to adjust the meter at least once a month by introducing this liquid.
After a few seconds check that the meter reads 4 o, otherwise you will have to calibrate it normally by turning a small screw until it returns to the reference pH value.
Each type of meter is regulated in one way, some require pH 4, others pH 7, and others require both.