a jones counter works well. but a bit of a nusance. you would need to have a known distance to calibrate it. like a 100 on the straightaway. preferably with lines. because without wheeling it down a line you will not be closer than 2 inches time to time. you need to calibrate it before each days use. because if you have a bike tire with air in it the different air temperatures during the day will change the measurement. but like they said, if you are an inch off at the 100. or even 5 inches off , you wont be able to distinguish that by time or race feel. since literally no one can run that straight of a line. one thing worth wheeling down the track a few times with a good wheel. which i believe the jones counter is, is you will find that no one ever really ties. because they wont travel the same distance within their lane from start to finish. but, once you have a known distance, i recommend a jones counter. but put some antennaes on your bike wheel down close to the ground so you start your measurement the same place. also think about a pace that matters to you. and calculate how many inches per second you are traveling at that pace. this will help you understand the tolerable tolerances of your inevitable inaccuracies.