Hanna Instruments? premium quality pH calibration solutions have an accuracy of ± 0.01pH at a temperature of 77°F (25°C). Each bottle of calibration buffer has a 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. With the color coded label you will be able to easily identify different buffer values. Discard buffers after each use for best results.