Gena, my wife runs the computer during the HAMB Drags, she has requested I post something she typed out about number placement: "Number placement should at least be on the left side (driver's side) of the car and as large and readable as possible. Numbers can be put on the car when you arrive at the track or you can help by already having your number on the car by either using glass chalk, printing it on a sheet of paper, using number stickers, having custom numbers made, or large magnetic numbers. If you do not have a window on the left side large enough to accommodate a large, readable number then please have it placed on the side of the car."