Hi Karsten,
thanks I would not have found the answer without your help.
There was still a problem with the variable P1 formula which just needed
an extra pair of brackets.
Just to clarify the [0] points to the first value in the numberarray ?
Also does this turn var Zt=[];into an array?
So again many thanks.

Brian yes the node is for Z(t) movement of your Variable Pitch Helix.
I just wanted to see if I could cut the amount of connections that
my original nod file had by doing the movement calcs within the node.
I've attached a working node.
Cheers
Barry