Cadency too low


I’m currently running Zwift on rollers paired with a couple of speed and cadence sensors (Garmin Edge 2), and have a few questions on how Zwift figures are computed.

First, the cadency displayed in the game is always lower than my actual cadency. To know it for sure, I did the test comparing a Zwift activity with an activity on my Garmin watch : Zwift displays an average 70rpm when my watch computes 100rpm. The difference is huge. My question is why ?

Secondly, the speed is inaccurate too.
I’m guessing this is intentional as rollers do not offer much resistance as trainers, but if this is the case, the speed is still way too high.
So, is there a way to

  1. Tweak my speed (only lower) to make the game more realistic.
  2. Or display my actual speed, so I can at least use objective number to improve.

Thank you

Same trouble here with cadence measurment…

Thank you for the link. Looks like I missed it when I did the search.
That is indeed the same issue, or at least, it seems very similar.

I guess it can be closed as a duplicate then.