20775991 Serial No. U26-001 Baseline Onset HOBO oxygen logger measures oxygen and temperature values. Onset Organizational HOBO Dissolved Optical Oxygen Sensor 20775991 0 - 20 mg/L; 320 to 95°F (0 to 35°C) mg/L HOBO Temperature Sensor 207759901 23 to 104°F (-5 to 40°C); non-Freezing 0.2 Degrees Celsius