how accurate is tacx vortex?

[jawaka]

I wonder how accurate this is?

Two reasons. firstly the speed indication compared with my wired bike computer on rear wheel is wildly out and possibly worse at low speed eg 8 mph on trainer 14 mph on computer although sometimes readings are more in agreement, I think at higher speeds

Secondly I have been using it on alps/pyrenees climbs and in real life I am using a 27/29 inch gear, on the trainer it's more like 45/50 and the time I am taking is far less than the real thing. In reality I should be taking 50% longer.

And I can't help but think it is overeading watts as it comes out consistently at 180 over an hour's climbing, but I'm not out on the bike on real roads very often , just go touring really . (I've barely been out as we have been looking after a grandchild all through the lockdown). I am 67 kilo and 66 years
The trainer says that it is properly calibrated.

Mind you I've worked hard on the trainer as I plan to go to the mountains next year and missing a year of getting fit seemed a bad idea.