I would like to create a time stamp on a spreadsheet such that when a
certain action occurs, I can simply tap on a cell (or a couple of
taps) to input the current time to the nearest second in a cell. While
I can use the =now() function to get the current time, it continually
updates, and all the =now() cells change (unsurprisingly) to the
current time. I want the time to remain the time I tapped the given
cell. Is there a convenient means to do this in Excel Mobile?

Thanks for your help.
Brian