Hanna Instruments pH 4.01 Calibration Solution 1 Liter HI7004Accuracy of + 0. 01 pH @ 25C Temperature chart of the actual pH value at various temperatures printed on each bottle Color coded label for easy pH buffer value identification Hanna calibration buffers have the lot number and expiration date clearly marked on the label and are airtight with a tamper proof seal to ensure the quality of the solution. Hannas line of calibration buffers has been specially formulated to have an expiration of 5 years from