I would like to add a counter to a power point presentation. Do you know if this could be done and how?

Basically here is what I would like to do: display a counter representing for example the number of cars rented since the beginning of my presentation. So for example, at the start the counter is at 0 and every minute is incremented of 2000 (this is just an example). We can see the counter on every slide, so at the end of my talk people can see (and I'll tell them) that since the beginning of the talk X(large number) cars have been rented.

I tried to find something on the internet but without success... I hope someone will be able to help me?