thank you everyone for your thoughts and experiences
i have been doing a bit more digging and reading around this
the original average HRV i quoted for healthy males in their 50's of somewhere in the 50 to 60ms range was from a google on my phone - but i have since searched several other sources and they mostly seem to agree with this number
eg here in graphical form
VIEW IMAGEhttps://elitehrv.com/normal-heart-rate-variability-age-genderon that graph it also shows the extremes - and mine is actually below the extreme low end for my age group of the 8,000 people in that data set - so it does look like mine is well below where it would be expected to be in an otherwise healthy person.
ref alcohol - the only alcohol i consume is from tinctures - but i go to some lengths to ensure the vast majority of it is evaporated off before i take them - so it should be minimal - less than 1 drink a day
next i looked into accuracy - and because the watch style fitbit and other similar makes of tracker - are not using electrical nerve signals as their trigger - like a proper EKG does - they will never b as accurate as electrode devices - like medical EKG or even sports chest strap type devices
several members on this Fitbit forum have however compared EKG type devices with their fitbits - and although there is some day to day variability - it seems the numbers and trends match up pretty well
https://community.fitbit.com/t5/other-charge-trackers/does-the-charge-4-calculate-hrv-accurately/td-p/4498519/page/5one thing to note - is with the fitbits - they only measure the HRV during the night when you are asleep - and the app then presents an average value in the morning - whereas other HRV measuring devices using electrical nerve signals - like chest straps - measure it in real time while you are awake.
sleeping and waking HRV are different - with sleeping HRV typically being higher - which is anything makes my values worse!
Blazer - i think this may be one of the reasons for you seeing a difference between the two - the Fitbit is an average of the night while you were asleep - and the chest strap is after you wake up