While the "finger tight" method gets plenty of people by, if you are unsure of yourself then get a dial indicator. Harbor freight sells a dial indicator and magnetic base cheap and it's definitely accurate enough to do a wheel bearing. While I haven't checked, I'm sure there are a dozen you-tube videos that explain how to use the dial indicator to check end-play.

Personally, I like to be absolutely sure it's within tolerance. I use the dial indicator every time.

Caveat: the Mercedes service manuals give the end-play tolerance specification in mm and the dial indicator that harbor freight sells reads out in thousandths of an inch. You will have to convert.