I want to turn a cell location in a the range definition in an MS
Excel function into a variable so that I can test a number of
alternative results.  For example, in the funtion

=average(a1:a30)

I'd like to the "a30" or only the "30" to refer to another cell, like
b1 so that if I change the value in b1 to say "a60" or "60" I can
change the range length in the function to

=average(a1:a60)

I plan to use this in order to do some tests on alternative moving
averages of a series of values to see which produces the best results.

I believe that you can achieve your desired result with the OFFSET
function, which returns a range and accepts cell references as inputs.

Taking your example of column A containing the data and using B1 as
the cell in which you input the desired range (30, 60, etc.), the
following formula should accomplish your task.

=AVERAGE(OFFSET(A1,0,0,B1,1))

I hope this helps,

anhebetude