Calculate difference between each column value and one reference value in a column

[cmm0685]

Hi all,

I would like to create a measure that creates the difference between a column and the first value of that column so I can display deltas between the first value (reference value) and the rest of the values.  For example, in Excel this would simply be:

where row 1 is bolded and serves as the reference value.  

I see that there is a "Variance" quick measure but that just shows the difference from row to row, not to a single reference value.  I have tried this approach but it produces all 0's when I add it as a column to my table:

ValueDelta = calculate(sum(Table[Value]))-calculate(FIRSTNONBLANK(Table[Value],[Value]))

To be clear, I would like the result to be a measure rather than a calculated column so that the result responds to slicers on the page.

Thanks for the help!
Chris