I went through this. My Vortex can read 20-70 watts high, and the higher the wattage the more it’s off. My FTP took a 50 watt chop when I got off the Vortex. I made a topic comparing my stages and Vortex.
One thing that set my Stages straight was doing a factory reset. That means removing the battery and shorting the terminals for 20 seconds. You can install the battery upside down for 20 seconds to accomplish the same thing.
This is a very informative video regarding the Tacx Vortex:
My Vortex can read 20-70 watts high, and the higher the wattage the more it’s off. My FTP took a 50 watt chop when I got off the Vortex. I made a topic comparing my stages and Vortex.