FTP calculation

I would like to know how the Edge 520 calculate the FTP.

On my first ride with it, here's the numbers for a 58 minutes ride:

Average power: 321w
Average power max 20min: 320w (how can it be lower than total average power, since it's the best 20 minutes ?)

Normalized power: 332w

FTP: 346w

Again, how can the FTP be way higher than max 20 minutes since FTP is roughly the same as a 60 minutes all out effort ?

Again, how can the FTP be way higher than max 20 minutes since FTP is roughly the same as a 60 minutes all out effort ?

was that the 520 FTP test or just a 58 minute ride?

It was on my first 58 minutes ride. If I remember correctly, right after the ride I saw "New record" or something like so on the 520, and the "new" ftp value.

On garmin connect, my FTP on some rides is 346w and for a reason I don't know it is 200w for some other rides.

Now I remember my 520 doing something similar. I hadn't expected that. I changed the setting to manually input my FTP. The calculated value was wrong, but not nearly as bad as yours.

Can you advise me how you actually input your FTP manually?

I would like to know how the Edge 520 calculate the FTP.

On my first ride with it, here's the numbers for a 58 minutes ride:

Average power: 321w
Average power max 20min: 320w (how can it be lower than total average power, since it's the best 20 minutes ?)