Fitbit vs Apple Watch Fitness

I got an Apple Watch (Series 3) just over a week ago. I decided that I will keep wearing my Fitbit, even though I will also be using the Fitness app on my watch to track exercise. I'm pretty attached to my Fitbit, as I've been using it for several years. I want to keep my records and milestones on it, and my friends list, plus I like the sleep tracker.

This morning, my friend Mike asked me if I had noticed much a discrepancy between the reading of the Fitbit to that of the Apple Watch App. I just checked (7:45pm) and here's what I found:

Fitbit:
20,040 steps
8.92 miles
100 Floors
2,054 calories

Apple Watch Fitness Tracker:
17,322 steps
8.11 miles
54 flights of stairs

Obviously, the Apple Watch tracks stairs differently, which isn't a huge deal. Almost 3/4 of a mile is kind of a big difference though, as is roughly 2,700 steps.

One thing I can think of that may have caused the discrepancy is that I went to Costco today. While at Costco, I was pushing a shopping cart most of the time. My Fitbit is clipped to my pocket, so it senses each time I take a step. My Apple Watch is on my wrist, which stays still when pushing a cart.

I realize this is not an exact science at all, but it is kind of interesting to compare the two side-by-side.

PS: I walked a lot more today than a typical weekday. Dick and I are trying to take a walks early in the morning before he goes to work. Plus, we are trying to take advantage of a beautiful day after the bad AQI, and in between rainy days.