The Onset MX2501 HOBO Bluetooth Low Energy pH and Temperature Data Logger is designed for long-term monitoring of pH in estuaries, lakes, streams, rivers, and oceans. Leveraging Bluetooth Low Energy (BLE) technology, Onset's MX2501 pH Logger communicates wirelessly with the free HOBOmobile app on iOS devices, making logger setup, calibration, and data offload quick and easy. A guided pH calibration process on the HOBOmobile app makes an otherwise complicated process easier to follow. The MX2501 logger dramatically cuts the time and effort needed to collect field data, while also offering higher resolution in data.