Sorry. me again...and I have been all over the wiki, mailing lists and manuals...

I have this:

\setlayer [progresssteps] % name of the layer
[hoffset=904 px, voffset= 28\nuggetnumber px]  % placement (from upper left corner of the layer)
{\stepstack}  % the actual contents of the layer

And I am hoping that as I increase nuggetnumber the voffset of the layer will be 28*nuggetnumber

I am setting nuggetnumber like this for the moment:

\def \nuggetnumber{3}

(in the other dev document it is the result of counter, so set dynamically) 

and this in the text

\nuggetnumber

which compiles to '3', so I assume the assignment is good to go.

varying both nuggetnumber and the scale factor (28) shift the layer up and down, but not in a way that suggests that 28\nuggetnumber is being evaluated as a product (so a scale factor of 7 and a nuggetnumber of 2 do not give the same output as a scale factor of 2 and a nuggetnumber of 7).

So I am led to think that there is something in the evaluating that is going wrong - data types / units? (if I hard code in the results I am expecting, say 28 px, 56 px or 84 px then I get exactly what I want...

Thanks, as ever

(Same result in ConTEXt ii or iv)
Ian