NatureSpirit Fingertip Pulse Oximeter: * Measurement range: SPO2: 35^99 Pulse Ratio: 30^250BPM * Resolution: 1% for SPO2, 1BPM for pulse rate * Accuracy: ±2% (70^99), unspecified (<70%) for SPO2; ±2BPM or±2% (whichever is greater) for pulse rate. * rechargeable battery to minimize ownership cost(a couple of years battery will recover the cost of the unit) and be green to the environment * Red LED display, excellent readability day and night * Only about one inch thick in size, one of the smallest