Which of the following can be used to calculate heart rate?

To calculate heart rate, you can use several methods, including: 1. **Pulse Measurement**: Counting the number of beats per minute (BPM) by feeling the pulse at various points on the body, such as the wrist or neck. 2. **Heart Rate Monitors**: Devices that can be worn on the wrist or chest that continuously measure heart rate. 3. **Electrocardiogram (ECG or EKG)**: A medical test that records the electrical activity of the heart and can provide an accurate heart rate. 4. **Fitness Trackers**: Wearable devices that monitor heart rate during physical activity. 5. **Smartphone Apps**: Some apps can measure heart rate using the phone's camera and flash by detecting changes in blood flow. If you have specific options or methods in mind, please provide them for a more tailored response.