Sum of average heart rate calculation showing a wrong value after a run.The total average the watch shows is 164 BPM whereas when i manually calculate the sum comes to 166 BPM average

I would be interested in how you calculate that. Really.

If we don‘t understand that, no one will be able to say something meaningful here.

Add the heart rate's shown at ever lap (kilometer in my case) by garmin .

The garmin total for average heart rate is 164,while if you add the above heart rate it comes to 166.33

Ok, now I get what you mean, thanks.

So, you simply add the average pulses per lap and divide it through the number of laps. But that is wrong!

This metric is time based, so you cannot simply say „a lap is a lap“, eg your last lap is only 20 seconds long! Also the other laps are not all the same length, but vary from 4:49 to 6:15

What you have to do (can be done in Excel): Take the average Pulse for a lap and multiply it with the time of this lap (eg in seconds). Sum up all of that values and divide it through the overall time.

The result is: 164,3!

TL:DR Garmin is right, you need to take the time into calculation

Thankyou so much for helping me out.