I’m currently using the Tacx Blue Matic Smart on Zwift and done some work on getting it calibrated as accurately as is possible.
Try all these things:
Set the resistance adjustment [via the cable lever to 3]
Inflate the rear tyre to the manufactures recommended pressure
Set the adjustment screw until it just touches the tyre then give it 3 full turns
Clamp the resistance roller in place.
Notes: The tyre pressure and degree of pressure from the adjustment clamping mechanism can make a massive difference to the numbers you put out when using Zwift. The trick is to be consistent so that, at least, one ride correlates to the next. Check your tyre pressure every few days. Tacx say the tyre should be “firmly” clamped…meaningless really…but warn that if you over do it you’ll damage your wheel.
At best this equipment will give you a means of roughly tracking your own training and a cheap way [they’re knocking them out at £99 in UK] of getting involved and getting fitter! For any more you’ll need a decent direct drive, fully smart setup…hope this helps, see you out there!.