TY-143 speed

[Mrnob]

Hello there i was just wondering why the speed change is so weird on these fans for me. Heres a pic:

Goes from staying around 600rpm to 1k then a big jump to 2.3

 

[Tealc]

I wonder if its because the fan is being controlled by both voltage and PWM. That could give skewed results such as this. It looks to me like the 20-80% values are all clamped at 650 ish.