Here's another way. Click in A1, then "insert","name" and "define". In the "names in the window" line type "k" and click OK. Back in A1, type the value that you want. Enter your data in column B, then in C1 type " = B1-k " (no quotes). Then drag the corner of B1 down.
I wish I knew a lot more about the program. It seems there's nothing it can't do.