PH meter is an instrument used to measure acidity or alkalinity of a solution - also know as pH. pH is the unit of measure that describes the degree of acidity or alkalinity. It is measured on a scale of 0 to 14.
There are different scales set by scientific rules to determine this. For instance, if the reading on PH meter is 7 then it is neutral. If it is above 7, then the element is basic and in the case of below 7 then it is acidic. So, this was the measurement criteria or we can say scale for checking the acidity or alkalinity.