Body Temperature is a fantastic app for iPhone and Apple Watch, by which you can measure your body temperature via heart rate.
You can calculate the temperature with the Apple Watch sensors or with iPhone Camera.
The app allows you to see all data in a list, and to see the last 7 data in a beautiful graphic.
Body Temperature uses HealthKit, it connects with the Health app to sync all body temperature data and heart rate data (write and read).
For a good measurement, when you measure the temperature you should stay sit and calm, so that you have a normal heart rate, and for the best precision you can also add a reference temperature with the associate reference heart rate. [...]