Ok, it's taken me a looong time, but I've finally noticed the little SM after the CR4 at the top of the page (see blow-up pic for those (like me) with grubby specs).

Having spotted it, I got to wondering what it meant. I thought about it a good deal (gave it a full 15 seconds), then tried Wikipedia, where all was revealed.
I thought of a few other possible meanings before, but I'm keeping them to myself!
Anyone else got any good suggestions?
BTW I'm marking this
before we start, 'cause it's got b*gger all to do with Engineering
.