High acidities accelerate the degradation of the paper insulation and causes corrosion of the steel tanks. Usually, it is suggested that the oil needs to be changed when the acidity approaches 0.3mgKOH/g, and when the acidity reaches 0.1mgKOH/g, the user should concern the acid number. KL632 Automatic Acid Number and Acidity Tester can help you monitor the acidity in oil.