Best way to create worksheet to show trend changes since last update

[Brandon2013]

I am trying to create a spreadsheet that displays data during a snapshot in time, with trending arrows indicating whether we’re up, down, or the same as last period.
My trend arrows compare the value in two worksheets “Current” and “Old”.

When a new month rolls around, and I want to input that data and then have the trend arrows re-adjust, I get stumped on the best way to do this.

The only way I can think of to accomplish this is to delete Old, rename the copy of Current to Old, and then input the new data in the Current spreadsheet.
But when I do this, all my formulas have #REF in the formula bar and I can’t figure out how to fix it.
I suspect the problem lays in the way I’m setting up the worksheet to begin with. I don't want to nor need to keep copies of each worksheet, data could be inputted at random times, and this is just meant to be a status board.

Does this make sense? Any ideas on the best way to do what I want to do?
I’ve attached a very simple sample worksheet to show what I’m doing.

Thanks.