I took some pictures of my Barnett rear sight and its marked 200, 400, 500 and 600 Yards in opposite to markings on yours. Mine's marked same as example in Skennertons BritishSniper page 22 which is of sealed pattern. Now why should yours be marked in a totally different way and have a crosshair reticle instead of sighting dot? Wheaty whats your example like?
I think I know the answer your Ulster Division sight is for an Ozzie LithgowSMLE as everythings upside down there isn't it?
Merry Xmas to all.