Watch workout distance accuracy -Carry iPhone or No?

Background.  I have been extremely frustrated with the lack of consistency with the distance as shown in the fitness app.  I have a v7 watch and a v14 phone.  They run current software. Both were upgraded 10.3 to 10.4 and 17.3 to 17.4 during this time period.  I have calibration turned on and I was carrying my iPhone when I cycled.

I used the “outdoor cycling” option when riding my bike in a suburban area with good coverage.  I ride the same distance (give or take 100 feet) every single ride.  I have been experimenting with carrying and not carrying my phone.  I have logged about thirty rides with my phone and fifty without my phone. The recorded distance with my phone varied from 10.31 to 10.90 miles.  The recorded distance WITHOUT my phone varied from 10.88 to 10.93 miles.

Having my phone with me causes such a margin of error I have stopped carrying it when I ride.

When discussing with a friend she was not comfortable riding without her phone which I understand 100%.  So I added a third option – carrying my phone powered off.  I have only done twelve rides in this fashion with the variance has been from 10.88 to 10.92 miles.  I will continue to ride in this fashion for the next three weeks to get up to a statically relevant sample size.

Bottom line of my testing – don’t have your phone turned on if you want to get accurate distances.