The Apera Instruments DO8500 oxygen meter is equipped with a state-of-the-art optical sensor for dissolved oxygen measurements. The optical sensor has no membrane and requires no special solutions. You can obtain a stable reading in 1 to 3 minutes. The sensor has a service life of up to 8,000 hours. The special coating on the cap protects the sensor from external influences and enables measurements regardless of existing light and chemicals. The meter is waterproof and dustproof (protection class IP57), allowing operation in harsh environments. The DO8500 features a memory function with space for 500 memory groups, which can be read out via USB. Technical specifications: Dissolved oxygen (DO). Measuring range 0 to 200%; 0-20.0 mg/L. Resolution 0.1/1%, 0.01/0.1 mg/L (ppm). Accuracy ±2% of reading or ±2% of saturation. ±2% of reading or ±0.2 mg/l (ppm), whichever is greater. Response time 90% in =30 s (25 ?). Calibration points: saturation point & zero point. Temperature compensation 0 to 50 ? (automatic). Air pressure compensation 60 to 120 kPa (automatic). Salinity compensation 0-45 ppt (automatic). Temperature measuring range 0 to 50 °C. Resolution: Accuracy ±0.5 °C. Other features: Memory locations: 500 memory groups (including time and date), data output. Power supply: 3 x AA batteries. Housing protection class: IP57. Dimensions: 88 x 170 x 33 mm (with case: 360 x 270 x 76 mm). Weight: 313 g (with case: 1.3 kg). Certification: RoHs, CE & ISO9001:2015. Scope of delivery: DO8500 measuring device. DO803 Optical Dissolved Oxygen Electrode. 2301-3M Conductivity Electrode. Electrode Calibration Cap. Electrode Clip. Small Screwdriver. Spare Water Reservoir Sponge. PC Link CD. USB Cable. Instruction Manual. Carrying Case. The meter is EC-marked and carries a three-year warranty on the device (two years on the electrodes).