I like the basic idea of the function. But I could imagine that a
solution should be made on the electronic level but not at the
mechanical level. I think about a module named "track&hold & change by
catch up" ;-)

Principle: the incoming voltage is given to the output until a trigger
(external or from a button on the module) happens. This trigger causes a
"hold" of the voltage. The voltage is held until the value of incoming
voltage "crosses" the stored value. It might be possible on analog
level, but would be assumingly easier with a digital solution.
A thinkable extensions might be:
* first trigger holds, second trigger enables the catch up change.
or
* first trigger holds, second trigger gives the voltage free immediately
(this can be achieved by existing modules already).


Florian