Fairly simple question about using time in Ada

["Chris Vinall" <cjvinall@dingoblue.net.au>]

I'm writing a program in which I need to be able to timestamp events and
then later check how much real time has elapsed since that event occurred.
It is essential that this timing operate to tenths of a second and
hundredths of a second would be a lot better.

How do I go about doing this in Ada? My textbook mentioned something about
Duration but was less than helpful.

Thanks for any help

Chris