Buy one of these...
http://cgi.ebay.com/ebaymotors/26-95...QQcmdZViewItem
Leave your car in first, power brake to 2000 rpm, let off the brake as you floor it.
If you do this on a flat level road, just after you hit 60, you can pull over and safely read the results.
It's not totally accurate, but it's close.
And it can help you to learn how to launch.