Okay, but how would you use a caliper, if the vehicle is so thin. The wider it is, the easier you can tell the numbers apart on a caliper and the more accurate. Would you just have to get a better caliper? I am using 1/1000 inch and it is not accurate enough. If I made it less than 20cm, it would not be close. How did you solve this problem?Use a rod with more threads per inch. They make coarse threaded rod, which is often around 20 tpi, which you might be using, as well as fine threaded rod, which gets up to 28+ tpi.How do you get it less than 20cm. Do you use wingnut to stop, because I do, and that is the narrowest I can get it with having enough room for the wing nut to reach 12 meters distance. I used wingnut and counting revolutions. Do you have any other ideas of how to brake. Also, is there electric vehicle in high school? Still active?