use Now() in two cells for start and finish times

I am trying to use the now() command in two cells (start and finish) similar
to a stopwatch. However, the latter overwrites the previous cell to the
latest time. Any help is appreciated.

Chip Pearson has a timer which might be suitable for what you want to
do. Here's the link:

http://www.cpearson.com/excel/ontime.htm

Hope this helps.

Pete