This is a measure of hydrogen ion concentration, or more simply, whether the solution is acidic or basic. Units 0 to 6.9 are referred to as acid or acidic. Units of 7.1 to 14 are considered basic and pH 7.0 is neutral. Takes 2 minutes. Range: 5.0 to 10.0; LM2159-01 range: 7.7 to 8.4 (Cresol Red).