My daughter was a newborn when Sesame Street appeared and she would recite that line in her car seat. Here I'm inspired to use it because the topic is: the so-called 'FBI Tilt' cited on the Kramer Holsters website.
I've already shown you that this carry angle is not ten degrees! So let's graphically show off the angles you think COULD be ideal, using a clip-on Myres holster that is from his earliest gunleather days which were the 1920s. I chose it because it's old, and the belt loop being on the front side makes it an easy 'eyeball' for everyone.
Above, the caption is by famed FBI agent Bill Vanderpool, the man who launched DeSantis' career as a holster maker.
Carry angle is technically measured with the pistol's sight plane completely vertical/90degs to the ground. We designers would measure angle from the fold of the holster ot the fold of the integral belt loop; I call this its 'bench angle' because we don't wear our trousers belts at a line parallel to the ground: they're tilted with the buckle closer to the ground. But that works out because our bodies cannot sense anything less than a ten degree change: we will unconsciously shift the holster along the length of the belt until it feels right. For me, with the carry angle set at 25 degrees, that is with a holstered 1911 set just behind the seam of the trousers (which is always, regardless of pants maker, at 3:00 on your body). That, for me and most slim people (think James Bond, which I'm not) is the most comfortable, places the grip most naturally to my gun hand as I reach back beneath my coat (even the Rangers wore theirs under a coat), and conceals best there because it doesn't 'print'.
All that assumes the holster carries at the ideal height, which for concealed holsters is with the 1911's mag button at the topmost edge of your belt, and for revolvers with the cylinder's length coplanar with the belt's width (like that, 'coplanar', that's patent attorney talk for 'on the same plane as each other', but shorter, eh?).
The holster has been rotated in my everyday software that's on all Windows computers; it begins with ZERO showing at the bottom of the image, then proceeds to 45 degrees which is then SOB territory but was 'the bomb' in the '60s.
Above and below, look hardly different, yes?
Above you can just begin to sense the angle increase.
Above and below, now we're getting somewhere. Professionally I have always used 25 degrees for both pistols and revolvers, and if you measure the old gunleather by Brill and Myres and Heiser you will see they used the same angle. One reason: both pistol and revolver present at their narrowest angle, side to side.
Above and below, 30-35 degrees, why not? Well, why?
Above and below you're in SOB territory.
Yes, I've seen up to 60 degrees! In vintage Seventrees and Gaylord holsters.
But the ideal, and the true FBI Tilt: 25 degrees negative caster --
Read more in my book titled "Holstory -- Gunleather of the Twentieth Century -- the Second Edition" that is available at www.holstory.com and printed for you/shipped to you in USA.