Quark is a portable heart rate monitoring device that monitors heart rate in real time through optical sensing technology. Ideally, Quark is able to provide more accurate heart rate data, and its accuracy can be affected by how it is worn, the quality of the bracelet, and other factors. When using Quark for heart rate monitoring, care needs to be taken to wear it properly and to choose a trusted and reliable brand. For important medical decisions and situations that require highly accurate heart rate data, use professional medical equipment for measurement.