lag in the DAC spindle output

[turbothis]

so if i start the spindle at half speed 700 rpm
it will ramp right up. no trouble

now when i move the slider bar down in rpm, it is real slow even though the DAC is maxed in the opposite direction to slow the spindle
then if i hit "OFF" it takes about 2 second stop stop outputting the DAC

why is this?
i am feeling like there is a lot happening other than my commands