I bought one a few years ago from a big name race team/car builder. It comes with a neat stowage box that doubles as a lunch box. You'll need that lunch if you are going to fill a tire or just even to add 5 pounds to a tire.

It is handy in the lanes as you can add a single pound to a 10.5 X 29 tire in just under 5 minutes per tire. Using this tool not only amazed my fellow racers, it amused them as well.

I only actually used it once, there just isn't enough time in life to use twice. I gave it away to a friend, who only used it once as well. It is now for sale, in almost unused condition, at a bargain price I might add.

I am told there is good ones of these available, I just haven't seen one. I now just plan ahead, and check or add in the pits. The only thing I regret in buying the one I had was throwing away good money.

Best of luck to you.