You can measure it with an ordinary caliper, but the problem is getting access. The timing chain needs to be continuously supplied with oil, so it is in rather

You can measure it with an ordinary caliper, but the problem is getting access. The timing chain needs to be continuously supplied with oil, so it is in rather than on the engine and can rarely be accessed without pulling the engine from the car. It takes several hours just to access the chain for inspection, so it's not something you'd periodically check - if you suspect a timing chain problem, you might as well replace it.