Chrony (brand name) makes several models of chronographs for just this kind of testing. The ones I've priced start at just under $100 USD and go up from there. With that in mind, I've found some used models in the past in good condition on Ebay here in the states for reasonable prices. It's worth a look if you're in the market. You may even check on your local Craigslist if you're in the states.