Power fluctuates

I’m on a Kurt Kinetic trainer, no power meter. The power displayed in Zwift fluctuates a lot. When I hold a steady cadence, the power displayed can fluctuate +/- 20-25 watts. If I do the same in Trainerroad, it fluctuates maybe +/- 5-10 watts. Not sure why that is.

Got a update this morning when logging into Zwift . Power is better does not fluctuate as much as the 1/15/15 update . Used to fluctuate up to 100 with my KK road machine now much better . Also appears the power is closer to what I would expect if working out with TrainerRoad . Keep up the good work guys . I actually look forward to getting on my trainer .

Bought another ant + stick . Direct comparison between TR and Zwift . 35 - 40 watt difference TR higher. But my comparison is not 100% accurate because I have a old steel road bike on my Trainer with 27 x 1 1/4 tire so my Circumference is larger than what Zwift is using . in 12.7 miles on Zwift - TR has me at 13.2 miles .