It monitors hemoglobin through optical reflectance principle. Sample can be 15-20 ul of venous or capillary whole blood. An H12 Hemoglobin Test Strip is used to get measurements in under 10 seconds. Measuring range is 4.0 to 24.0 g/dL. It can store 250 test results and is factory calibrated based on ICSH. It performs self-check and auto-judges and displays malfunctions. It's powered by 2 CR2032 Batteries.