It's a 5k ohm pot with the sensor arm on the wiper.. It's anolog but I don't
know how the control unit deals with that..

I have been trying to get one on ebay.. They show up about once every week
or so and end up going for about $150 each.. The ones I have seen were new
or factory refurbished.

Your ST4000 will work without it, according to what I read in my ST5000
manual. You just have to note the absense in your configuration routine.

Steve
s/v Good Intentions