ORP: -999mV ~ +999mV. TDS: 0-9999 ppm; 10.01-200.0 ppt. Turn on the Bluetooth function: After the water quality pen is turned on, there is no Bluetooth logo and it cannot connect to Bluetooth. You need to press and hold the power button for 5 seconds, ，and then you can connect to Bluetooth after the Bluetooth logo appears.
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