2 stepper cnc inaccurate
I forgot to take care of negative steps in remainder accumulation.
This solved it.
// x accum
float resX = mmX * (float)X_STEPS_PER_MM;
float lresX = (long)resX;
_x_acum += resX - lresX;
    
long extraStepsX = 0;
while(_x_acum &gt; 1.0f){
     _x_acum -= 1.0f;
     ++extraStepsX;
}
    
while(_x_acum &lt; -1.0f){
     _x_acum += 1.0f;
    --extraStepsX;
}
// move stepper for lresX + extraSteps