Check the listing for details. Milwaukee MA9004 pH 4.01 Calibration Solution. Condition: New. Listed at 19.99 USD. DESCRIPTIONProbe calibration is a simple procedure for optimal performance and should be done any time your readings become suspect. Calibration should be performed at least once a month.MA9004 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 buffers.Milwaukee solutions are designed to help you achieve reliable and repeatable pH measurements while extending the life of your electrode.DESIGN FEATURESpH 4.01 Calibration Buffer Solution (230 mL)Fundamental for the correct use of electrodes and for obtaining the most accurate and reproducible readingsSealed against light with air tight, tamper proof capIdeal for fast calibrationSimply open, pour into a beaker or container and insert the tester or electrode to start the calibration process.