Calc formula/ code help

Hi I am writing this for a family member, I have also added a image to help me.

He wants data 2 to be subtracted from data 1 and shown the answer in the next row of data 2.

he will be adding to this sheet every month so I’m after a code that will repeat the said formula.

Sorry if I have not expand myself feel free to ask any follow up questions

“he will be adding to this sheet every month so I’m after a code that will repeat the said formula.” How will this be added? Are lines 3-4 a repetition of the model of 1-2? OR is line 3 the Feb data that gets subracted from “Data1” as well? Much copy/paste in calc with “autoadjust”, but the pattern you have in mind will make a difference. Can you explain how the next set of rows will appear?

Write in the cell in what you want the answer.

=B1-B2