Date set to date the worksheet was last modified

Mr Excel

This should be an easy one for you - if it is possible

I work on spreadsheets daily and then save them to
refer to them later or update them. What I would
like to achieve is :

When I actually work on a spreadsheet (not just
open it)- the date that I last worked on it will
automatically be recorded and only changed should
I update the contents of the worksheet

What I am trying to achieve is the last date that
the file was modified ie the latest file and to
preserve the date unless I modify the data.

Is there perhaps a Macro could use (I am well versed
at programming in Qbasic if this can be used)or is
there some simpler way as I don't intend getting
involved in Visual bacic and Excel programming.

I thank you for any assistance that you are
able to offer

Regards
Stephen Allenberg