The pen ORP meter is professional and ideal tool for testing your water level. Suitable for aquarium pool and environment water. Features: Use to measure the amount of Oxidation Reduction Potential (ORP) level. The tendency of the solution to either gain or lose electrons. Clear LCD with backlight. Apply in water sources aquarium hydroponics spas swimming pools and other water systems. Compact and portable pen-type design. Easy to use and provides instant display of results. Specifications: : -1999mV ～ 1999mV Resolution: 1mV Accuracy: ±5mV Operating : 0℃ ～ 50℃ (32°F ～ 122°F) Battery: 4 × 1.5 V (AG-13) Button Cell Battery (not included) Color: Green Material: ABS Item Size: 15.1 * 3.3 * 2cm / 5.9 * 1.3 * 0.8in Item Weight: 52.4g / 1.8oz Package Size: 17.8 * 7 * 3cm / 7 * 2.8 * 1.2in Package Weight: 108g / 3.8oz Package List: 1 * ORP Meter (Battery is not included) 1 * User Manual 1 * Screwdriver