I have an Active 2 watch, if I measure my heart rate on watch always shows a higher number and if I immediately check using my s10, it shows at least 10 to 15 counts lesser. I compared it with my fitbit too. Fitbit and s10 reads similar number where as Active 2 is elevated by 10 to 15 counts.
Samsung Health measures your heart rate using lights and sensors located on the back of your watch. But you’ll need to make sure you're doing things properly to get the best measurement results. Check out the following information:
For a mid-workout measurement, take a brief break before taking your heart rate.
Take measurements when seated and when you are relaxed for the most accurate reading.
Do not move your body while taking heart rate measurements. Doing so may cause your heart rate to be recorded inaccurately.
If the measurement is very different from the expected heart rate, rest for 30 minutes and then measure it again.
If your heart rate is extremely high or low, measurements may be inaccurate.
Wear the watch snugly above the wrist. Do not fasten the watch band too tightly. Avoid attaching third party bands to your watch, and only use the band included with your watch.
Measurements may need to be repeated at least five times for the most accurate results.
Remove the protective plastic from the heart rate measurement sensor before taking measurements.
If the heart rate sensor is not working properly, wipe the sensor and adjust the position of the watch to sit above your wrist.