I have my Garmin 830 and Zwift connected to my Elite trainer. What bugs me is that my Garmin unit constantly shows approximately 25 watts more all the time! Why is that? Is there any fix to that? Or am I thinking wrong here, that they should be matched?
I have had the same issue for years. The truth is that Zwift software has never really been about accuracy it’s only about creating a fun environment. I wished this wasn’t the case but it’s true. I tried early on to get Zwift to fix this back when they had a help desk. They got tired of not being able to fix things so they eliminated their tech support and instead rely on user forums.
are both looking at the same power source?
I have seen that when, for instance, Zwift is getting power source from the trainer and the bike computer from a power meter… do you also have an additional power meter?
Okay! Not the answer I was looking for but nice to know I’m not the only one with this “problem” 
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They are both connected to the Elite trainer.
Connected with ANT+ and Bluetooth? There were some reports about different power numbers readings, depending on the connection.
Interesting! What’s the “best” connection to get a accurate reading on both?
Your trainer is one power-measuring device.
What is your secondary power meter (cranks, pedals?).
Or are you saying that you only have one power meter (your trainer) and the data is being sent to both Zwift and a Garmin head unit and these two power values are always differing by 25 Watts?
Yes! That’s exactly what I’m saying!!
At the end of the whole activity, I would guess you have a garmin activity and a zwift activity? Does that same 25 watt difference show on the whole ride’s average?
It’s possible I suppose you could have Zwift set to show instant power, while the garmin is set to show you average 3, 10 or even 30-second power?
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I’d record as well on your Garmin and run it through the analysis function on Zwift Power (under your profile view) to compare the two files. That way you’ll know if it’s recording two different sets of numbers or if it’s a display issue as mentioned above.
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I’ll have to check, didn’t think of that! Thank’s 
Found this now
But your write Garmin is reading more, and
I expect Garmin is ANT+?
Try what @B_Jimmy recommended - analysis tool at Zwiftpower.
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That’s a great article. Thank’s for sharing!
You will also note that using a Garmin on an Elite Trainer will have different power readings due to the head unit having different calibration settings .
Mine are way off for my Drivo and there is a page on the Elite website which tells you how to reset the Garmin values for accurate power per trainer .
I still cant get mine to match power and or distance.
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