Most every taxi firm in the uk has a piece of plastic water pipe and a bunch of ping-pong balls. As each driver comes back they take their number from the basket and drop it into the far end of the tube. The next call that comes in, and the despatcher takes the ball out the "near" end.
It is an almost foolproof FIFO pipe (literally), simplemfor everyone to understand and very cheap to run.
It is an almost foolproof FIFO pipe (literally), simplemfor everyone to understand and very cheap to run.