Last sheet update date

Hi There, I want a formula for a cell that will update with the date according to the last time a cell was updated.

ie: I have a table (table A) that I update from a pivot table that Brings data from a daily data source. There are several people on the team who may go in and update the results on a daily basis and every day we change the date so that we can tell when it was last done and if it needs doing.

I want the date field to update automatically when I update the data, the pivot table and hence Table A.

Any Ideas?