Zone minutes calculation random and absurd

[RoBoy]

I am an older male.  I take the same 2 mile walk every morning.  The walk has some good long inclines and declines on it.  I can feel the effort on the inclines.  Zone minutes are important to me as I am a recovering heart surgery patient.  Yesterday, my Charge 6 device recorded 1 zone minute after the 45 minutes +/- of my walk.  Today, it recorded 53 minutes.  This discrepancy is typical of the log that my device records.  I wear the device on the same wrist, at the same band hole.  I switched out of an older Inspire model early this year as I thought perhaps it had outlived its usefulness.  Sadly, it was a waste of money; although I do enjoy the bigger display of the Charge 6...

[LZeeW]

Hi @RoBoy.  Active zone minutes are heart rate based.  The equation is a little complicated, because your resting heart rate is part of the equation.  Fitbit calculates your zones using your age and resting heart rate, but your zones can change on any given day if your resting heart rate changes.  In addition, your measured heart rate can change from one workout to the next, depending on circumstances.  Working out in warmer weather tends to have a faster heart rate.  You could be overdressed or underdressed for the weather and that can change your heart rate while exercising.  I don't do the same walk every day, but I do get a wide range of zone minutes for comparable walks in my hilly neighborhood.

Please look at your heart rate details for some of your walks.  The graph shows your heart rate and your zone on that day.  Active zone minute calculation isn't fuzzy math, like sleep scores seem.  It has a real equation.

[JohnnyRow]

Oops - I just realized @LZeeW has already given you a good reply to this.

You can figure out the difference yourself to see if it really is a problem with the Charge 6.  Zone minutes are based on heart rate,so look at your heart rate graphs during the 2 walks.  First see if they even look reasonable or does one of them have obviously wildly inaccurate graphs.  If they both look somewhat reasonable, compare to the lower limit of your "Moderate" heart rate zone.  That is what it takes to get Zone Minutes.  That value is going to be different for everyone.  If you don't know yours, tap your Zone Minutes circle and scroll down and it will show the heart rate limits of each zone.

For me that limit is 93.  If I get my heart rate up to 93, I start earning zone minutes. But if I take a long walk and my heart rate stays at 92, I wouldn't get any zone minutes even though there really is negligibly difference between 92 and 93 heart rates.
So see if maybe that is your difference.  It could be both walks your heart rate is near the limit to get zone minutes.

[RoBoy]

Thanks; I may look into it, after I get over being irritated at the
whole thing.

[RoBoy]

Thanks for your thoughtful reply. I closely watch my ZM and based on my
daily experience, I just do not think more "work" looking into the Fitbit
calculation is worth my time. The results I get daily vary way, way too
much for there to be some reasonable explanation. Yesterday for instance,
the exact same walk, at the same time of day with the same kind of
clothing, at the same pace, my device logged in 1 ZM for a 45 minute walk
with regular long inclines. Today on the very same walk/conditions, it
logged 56 ZM.

But again, I do appreciate your feedback.