M10004B is a lab grade pH 4.01 buffer solution certified to meet the standard to an accuracy of +/-0.01 pH removing the inaccuracies involved with mixing calibration solutions from powder. Sachet packaging means that you get fresh solution every time. Ideal for infrequent or field use. No risk of using expired calibration solution. Milwaukee solutions are designed to help you achieve reliable & repeatable pH measurements while extending the life of your electrode.