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Hey there @weeeone, thanks reaching out the Forums. Welcome! 
Thanks for sharing those details on your post. I'd like to mention that your heart rate may be affected by any a number of factors at any given moment. Movement, temperature, humidity, stress level, physical body position, caffeine intake, and medication use are just a few things that can affect your heart rate. Different medical conditions and medications can impact your heart rate as well.
When your heart beats, your capillaries expand and contract based on blood volume changes. PurePulse LED lights on your device reflect onto the skin to detect blood volume changes and finely tuned algorithms are applied to measure heart rate automatically and continuously. The heart-rate icon you see on the display tells you if you're in 1 of 3 heart-rate zones.
Your tracker can have difficulty finding a signal, typically due to the tracker's fit. For example, wearing your band tightly may constrict blood flow in your wrist and affect the signal. We recommend experimenting with how high you place the tracker on your wrist. When you're not exercising, wearing the tracker just above the wrist bone as you would a watch typically works fine. However, moving the tracker up a couple inches can be helpful during high-intensity exercises or exercises that cause you to bend your wrist frequently. If you haven't already done so, please review our recommendations for wear and other tips shared by @SantiFitbit.
If you're wearing the tracker correctly but you feel it is not the correct readings, try restarting your Surge and keep an eye to future readings.
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