[sdiy] Tapped Pots?

[Tom Bugs]

Hi all,

I'm wondering if anyone can shed some light on pots that have an extra 
lug for a tap point.
I've not been able to locate any real info about - i) how the resistance 
is 'arranged' within this setup ii) typical usage
- have checked several datasheets and done some googling, but no luck yet.

The main thing that makes me look at them is for bipolar attenuators -- 
I've used some centre-detent pots before but these tend to have some 
slop in the middle and I generally have to use an onboard trimmer to 
dial in the centre null point.
Would tapped pots help?

Cheers!
Tom / BugBrand