Secretly Track Changes To Cells?

I have been given a spreadsheet from a customer. They want us to use this spreadsheet to bid on projects. This is the most sophisticated Excel document I have ever come across.

I came across some hidden columns that are labeled Prev. Total. Is there any way for Excel to track changes that are made to values of cells? In other words, is there any way for Excel to somehow record that someone first entered $1 into cell E1 and then later entered $2?

Thanks, Spence