When binding handle in a Viewer State, I have set cache_previous_parms to True, how can I read those previous parms back in to do something?

cache_previous_parms

If True, the handle retains a record of previous values. This can be useful if you want your code to calculate deltas as the user moves the handle, for example to know how fast the user is dragging the handle.

Precisely what I need is to calculate the delta.

The previous parm values are stored in the "prev_parms" entry of the kwargs dictionary passed to onHandleToState

https://www.sidefx.com/docs/houdini19.5/hom/state_handles.html#dynamic-handles [www.sidefx.com]