Visitor Counter with PHP

I would like to use fake dynamic visitor counter with PHP. I know rand(), function, but at every time I refresh page random digit can be anything.

I want the number to be run 500-2000 so it won't increase beyond 2000 and neither decrease below 500 and not instant drop from 800-500 it should be increase +5 to -5.

How can I achieve that with PHP?

Thank you!