Copy column to automatically update in Excel

I currently have a column of numbers in, say, sheet A. I'd like to copy this column to sheet B which is easy enough.
However, if i make a change to a value in the column in sheet A is there a way to make the value automatically alter in sheet B? (I am working on a Mac but answers in either Windows or Mac would be helpful).

Currently, sheet A is a long list of numbers and sheet B is identical with the duplicates removed. If I add a new value into A I would like this to automatically appear in B.