Charge 6 off by more than a mile for a 4 mile run

[kcob99]

The difference is not a tenth of a mile here or there.  Ran 13.1 and the Charge 6 had that I did 8.5. I thought the watch was set for my stride. I recently replace my Charge 2. Never noticed a difference, such that I did not think about how it calculated my stride.  I thought the Charge 6 would do the same. I did not intend to have to turn on the GPS every time.  

The instructions said it can calculate based on stride.  That did not seem to be the case.  It was off by more than a mile for a 4 mile run.

Do all workouts have to use the GPS?

Moderator edit: clarified subject.

[Triletics]

I can only say that Charge 6 is horrible at estimating the running distance. Not even one run it tracked even remotely correctly for me (using GPS which anyway never works). It's not a wearable for runners.