Best method for a monthly archive of a worksheet..
 

Greetings, I am just looking for input as to what methods people use to
archive spreadsheets on a monthly basis.

Here is the scenario, a coworker runs speadsheet she wants to archive
monthly so she does a 'save as' to give it a new name from her master sheet.
She has formulas that refer to other sheets in her spreadsheet. When opening
up the archived sheet of course she gets the 'do you want to update'
question. The worry is that someone will say yes and thus change the data
that we want saved as a snapshot in time.

What methods do people use to archive a sheets on a regular basis.

(We talked of copying the whole sheet and then "pasting special...values"
overtop of itself, we have also talked about saving as a pdf.)