Product Name: R8APP: Smart Health - Features: Exercise measurement, sleep monitoring, multiple exercise modes, heart rate measurement, blood pressure measurement, blood oxygen measurement, automatic health monitoring, activity information data storage, historical data storage duration, remote control photography and other functions Product model: 22 #, ring outer diameter 28.5mm, ceramic inner diameter 26.5mm, ring inner diameter 21.5mm - Product model: 20 #, ring outer diameter 26.5mm, ceramic inner diameter 24.48mm, ring inner diameter 19.8mm - Product model: 18 #, ring outer diameter 24.5mm, ceramic inner diameter 22.48mm, ring inner diameter 17.8mm - Product model: 16 #, ring outer diameter 22mm, ceramic inner diameter 20mm, ring inner diameter 15.45mm