I can't seem to get this function to work... any ideas?

Function mirror(rng1 As Range)
Application.Volatile
Application.Caller.Cells(1, 1).Interior.ColorIndex = rng1.Cells(1, 1).Interior.ColorIndex
mirror= rng1.Cells(1, 1)
End Function

I just want one cell to mirror / track / duplicate another cell, including the formatting and contents, whatever that might be.

For testing purposes, I'm happy for it to track the background color plus the contents, but in the end, I want it to track the full formatting / alignment / border as well as the contents.

Essentialy, I'm going to have a row of 50 cells with this function mirroring a row further down the worksheet.

I guess the only other way to do it would be a copy&paste within the worksheet_change method, but I can't understand why the above doesn't seemt to work.

thanks
Guy