Why my TP is going down after an outside ride with two Breakthroughs? I don’t think I understand everything yet.
Your signature will float up and down based on changes in Training Load (TL) and signature adjustments from Breakthroughs (BT events).
A BT includes one or more changes to your three fitness signature values.
A BT can adjust a value down to align the numbers with the signature algorithm.
That was a silver BT with two values going up and one down.
If you don’t agree with a BT adjustment you can flag the activity which retains the strain analysis but skips the signature calc.
Your signature is recalculated after every activity or lack thereof (signature decay).
The goal is for your signature to be in the right ballpark for training purposes.
You can monitor your TP trend up/down over time by viewing XPMC under the Progression tab.
If you aren’t confident your signatures is dialed in yet, I suggest riding this fitness test workout entirely in Slope mode when your form is fresh. Exceed targets if able and make sure to ride to a complete failure point on the final interval. Or perform similar intervals outdoors – two short max sprints, rest, then escalating intervals above TP (without full recovery) until failure.
Reference –
Ok, thank you. I will try it with the fitness test.
The BTs were already fine. If I understood you correctly, this will settle in and the TP will then go up again. I was just surprised because my last FTP ramp test on zwift was at 164.
Perfect opportunity to mention our last Tech Support FAQ video:
The change in signature represents what your fitness was on that one ride. Try and hold on a bit longer or push a bit harder at the end next time to get those couple of watts back! 
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