Need a Javascript "count up" timer that displays fractions of an hour

I need a lightweight javascript that will accept input as an hour (or a fraction of an hour) and then count up from there.  E.g. I pass input of 2.3471 hours to the function and once the webpage loads the value starts incrementing every second on the page.  I'm sure there is someone out there that can point me to a good function.  I wasn't able to google anything, but i'm sure i'm not using the right keywords.  Can someone clue me in?