Feature: Compact and portable pen design,easy to operate and storage. Large and clear LCD, easy to read and accurately measuring functions. The tester is made of high quality electronic components to ensure high accuracy. Suitable for water sources, aquariums, hydroponics, swimming pools and other water systems. The resolution of ORP tester is 1 mv, very high sensitivity. Specification: Model: ORP-169 Measurement range: -1999 - 1999mv Resolution: 1 mV Accuracy: 5mV Operating voltage: 4*1.5V (AG-13 battery) (No-include) Working temperature: 0- 50 Correction: 1 point correction Product dimension:188*35*35mm / 7.4*1.4*1.4in Weight: 290g / 10.2oz Steps: 1. Remove the protective cover. 2. Touch the "ON/OFF" switch to turn on the power. 3. Put the electrode into the solution to be tested, shake it gently, and read the displayed value after the value is stable. 4. Touch the "HOLD" button to keep the current measured value. If you need to re-measure, press the "HOLD" button again to automatically release the hold status. 5. After use, press the switch, wash the electrode with distilled water, and put on the protective cover. Precautions: 1: There is a white crystalline salt around the electrode, which is a normal phenomenon of the ORP electrode. Only when the electrode is immersed in clean water, it dissolves and disappears. 2: When testing the ORP value, it usually takes about a few minutes to about 10 minutes. Wait for the value to stabilize and jump very slowly or read the displayed value as the measured value. 3: The display value in ORP and air is jumping, it is normal phenomenon that there is no regular change. 4: After use, please turn off the power, wash the electrode with pure water or distilled water, use a soft tissue to dry the water and put on the protective cover. Package list: 1 * ORP Tester 1 * Installation tool 1 * User manual Note: The actual product color may deviate from the photo due to light. There may be a slight deviation in the measurement of product.