click-and-rotating knobs

[mattwatts15]

I have an array of knobs, they all have functions so that you can click-and-drag left-right or up-down to make them rotate back and forth.
when i have one knob on its own the code works fine. but now that i've put them in an arrary i've confused myself with the code.
i have a var currentKnob:MovieClip
and a var KNOB:MovieClip
the reason i have a currentKnob var is so that when i'm tracing the click-on knob, as3 will know which one is being clicked.
i've got confused on where i should include currentKnob in the functions, and where i should include KNOB in the functions.
i think just by looking at the code someoen can probly figrue out where i mixed the two up, but i have tried lots of combinations mixing the two up and keep getting the same error:

TypeError: Error #1009: Cannot access a property or method of a null object reference.
	at knobs_fla::MainTimeline/frame1()

thanks for any help