Just completed my 10th sector this year.
Seems the process goes like this:
If you need to check in: ALL bags near the limit must be placed into the metal measuring rack. If it doesn’t fit then you have to pay to have it placed in the hold. There are no exceptions t seems!
If you check in online: It seems a visual check is all that happens here. You can get away with a bag slightly larger than the dimensions. Be careful though, as a few times i have found "online checkin" not available at foreign airports and having to checkin at the desk (where they asked me to place the bag in the rack). The one bag rule is definitely enforced!
The rack does seem very tight. If you have a soft suitcase (like mine) then its easy to bulge in the wrong place so it will not fit. Also be careful that published luggage dimensions usually do not include the wheels!
I will measure the rack next time I’m at the airport (my second home!)
Smala01