"....Facebook Group page one person is adamantly claiming....."

Lots of self appointed "experts" on Facebook. This particular one is either totally unread or uneducated/ignorant and does not wish to learn. ie: thick as a brick and proud of it.

All one would have to do (if they did not want to actually research for themselves) is initiate a polite contact to any of the current British gunmakers to confirm that the sights are marked in YARDS, or in the case of Continental makers probably in METERS.

As an historical aside, the leaf sights to 500+ yards were not mere window dressing. Back "in the day" (particularly in South Africa) it was acceptable to blaze off at a herd on the plains that might have been 500 yards away and too hard to stalk closer......if an animal went down, that was all that mattered. Not sporting at all by todays standards, but back then it was business as usual.
- Mike