How accurate are Apple Watch calorie calculations?

Have noticed for the last three Apple Watches that if I forget to turn on one of the Workout modes I accumulate far less calories burned than if a Workout was turned on. Decided to run a test today. My previous watch had the usual planned obsolescence shorter battery life but I charged it up and wore it on one wrist and my current watch on the other while building fence line on the ranch. Pretty strenuous activity. One watch had a Workout turned on and the other didn't.

As expected, the Workout On watch showed I burned 996 active calories by noon while the other one showed only 389 active calories, and only 24 minutes of exercise. Strangely enough though, the Fit app on my iPhone showed 1,224 calories burned during the 3.5 hours of exercise vs the 996 Active calories in the Health app for the 12 hours since midnight including the 3.5 hours!

I am very conscientious about my calories and exercise and have kept a calories burned/consumed spreadsheet for years. Now I'm wondering if all my data as gathered by the Apple Watches is way off compared to the Fitbits I wore before Google bought them. I saw a peer reviewed study that said the Apple calorie calculation averaged 27% high. Is this true???? Help!

[Re-Titled by Moderator]

Original Title: Big calorie discrepancy in devices.