Sper Scientific dissolved oxygen pen. Dissolved oxygen analysis is routinely performed in environmental testing, labs, industrial and municipal waste water, aquariums and fish hatcheries. This Sper Scientific dissolved oxygen pen is easy to carry, simple to calibrate and use. Sufficient for many surface dissolved oxygen measurements. Includes a soft carrying case with belt loop, two spare probe heads, electrolyte and 4 AAA batteries. IP-67 Waterproof. Simple one-hand operation. Automatic temperature compensation. Automatically calibrates to air. Easy to replace pop-off probe heads. Simultaneous display of dissolved oxygen and temperature. Hold and minimum/maximum recall. Grade level: middle-high school. No allergens. No choke hazard. 0 to 20.0 mg/L range; 0.1 mg/L resolution; +/-0.4 percent mg/L accuracy. 32 to 122 degree F range; 0.1 degree F resolution; +/-1.5 degree F accuracy. 0 to 50 degree C range; 0.1 degree C resolution; +/-0.8 degree C accuracy. CE Approved, RoHS Compliant.