http://groups.google.co.uk/group/rec.audio.pro/browse_frm/thread/4a9bac0f8d3534ed/5bccafba1f79ebe1?q=You+can+change+the+center+frequency&rnum=1&hl=en#5bccafba1f79ebe1
In fact do a search on Paul's user id at rec.audio.pro to find lots of good things about API...
http://groups.google.co.uk/groups?hl=en&q=&enc_author=0o5fxxMAAAB2m1cPQsbTMccDqCZ4qTyNWMj6vob75xS36mXc24h6ww
(oh - and I heard that about the centre detent log pots - a man can make a few mistakes - well about 50 of them...! cheeky boys!!)