SpO2 measuring range: 70-99%.nnAverage Root Mean Square (ARMS) of SpO2 accuracy: 80%∼99%: ±2%, 70%∼79%:±3%, <70%: no definition. Pulse rate measuring range: 30-250bpm. Pulse rate accuracy: 30∼99bpm: ±2bpm, 100∼250bpm: ±2%. * When does the battery light indicator appear in the display? The battery light indicator appears when the battery is low.