How does counting down a Rat-L-Trap work?  seconds=? feet.  

What the countdown method is, for every second the lure sink aporx. a foot. This way you will know where to start your retrieve depending at what depth you want it.  So when the lure hits the water you start counting "one mississippi, two mississippi, and so on. Then start your retrieve after you "counted it down" to where you want it.

2-3 feet per second

And the answer is: a regular 1/2 oz Rat-L-Trap sinks at a rate of 1 ft/sec.