spindle speed not stable in bouth direction

Spindle speed is not stable on bouth directions.

Encoder has 1024 lines.

I set counter-mode to true.... if i set it to 0 (false ) quadrature mode then i get 4x biger RPM.

I use mesa 5i20 and 7i33 analog card.

Also i have tried speendle with potenciometer but results are the same.

Any ideas how to solve problem?

If you have a quadrature encoder I would run in quadrature mode.
You change the encoder scale to fix the 4 x issue (if you set encoder scale
to 4096, encoder velocity will be scaled in RPS)

What amount of speed variation do you see? there will always be some variation.
sometime people filter spindle speed via the low pass filter component
so the displayed speed is less jumpy