Take a look he

http://www.mcgimpsey.com/excel/timestamp.html

In article ,
"Sami Euren" wrote:

If =now() fuction is used in a cell, and cell is formatted dd.mm.yy hh:mm,
time is updated every time sheet is calculated. Like this you have exact
information, when latest change was done. Problem is, that it changes the
time every time sheet is opened also, and data is "lost". What would be the
easiest way to save the latest time when change to sheet was done ? Is it a
function button, that copies only the time value to another cell or what ?

-Sami