Fill down from D1 to active cell in excel ??

Question

Hi all. I am trying to write a script to take the values from column A and subtract the value of A$1 from the rest of column A. To do this manually I set D1 = A1-A$1 and then fill down in column D to the last used row in column A. Then copy-special paste values from column D to column A. Below is what I have written so far, but the "select (ranges "D1" thru active cell)" selects cells D1 and the active cell ($D$5) not from cell D1 down to the active cell.
Any ideas for a newbie?
tell application "Microsoft Excel"
set formula of cell "D1" to "=A1-A$1"
select (get end range "A:A" direction toward the bottom)
set theEnd to (get first row index of active cell)
select cell 4 of row theEnd
select (ranges "D1" thru active cell)
fill down (ranges "D1" thru active cell)
end tell

Answer 1

I figured out a way to do what I was after, but I would think there is a more direct way of doing it.
If anyone has a way to slim down or clean-up this script, please let me know.
Here is the script I have now.
tell application "Microsoft Excel"
set formula of cell "D1" to "=A1-A$1"
select (get end range "A:A" direction toward the bottom)
set theEnd to (get first row index of active cell)
select column 4 of row theEnd
set lastRow to "D" & theEnd as string
set range1 to "D1:" & lastRow
fill down range (range1)
end tell