Deployant buckles are lovely.
Not only are they a little more 'tech' than the usual tongue-buckles, but they have some useful advantages too: both parts of the strap are connected together by the deployant buckle, so when you undo your strap, it's still looped around your wrist, so it can't easily fall on the floor. Also, once you've set it to the right size, it clicks closed to that size every time; you don't have to haul the strap through the buckle when you put your watch on, wearing the leather prematurely.
To adjust a deployant buckle, pull on the pointed end of the strap to open it.
Then, look at the part of the buckle with the EB shield logo on and you'll see a D-shaped section underneath, against the inside of the strap. Unclip that by lifting the curved part of the D with your thumbnail.
Now, slide the buckle until it it looks about the right size (the 3rd hole from the end of the strap nearest the watch is probably about right), line the post up with the hole, and click the D-shaped section closed.
Slide your watch over your hand, and notice how the buckle now clicks closed to the right size every time...