Saw this on Amazon:
Actually a different product, but had the same/similar reticle.
I was curious as to why these specific degrees are measurable. I get why 60 degrees might be broken out, but what is special about the other three (29, 55, 118)?
Probably not the answer you’re looking for…but…
In my collection of crap, I have a cardboard box, which contains a promo publicity kit for the movie Cool World. The box is of obscure angles; every face is an irregular quadrilateral. It’s the weirdest damn thing. And the printing company that created it was working from blueprints that specified all those odd angles!
Pretty sure it’s 25, 55, and 115.
WAGR (Wild ass google results).
perhaps they are the most common in use , that are not multiples of 5. (well 55 
I am giving the rational for going to the effort, the actual result may contradict me…That is, the reason that 55 got there MAY BE that they were looking for angles in common use that were not a multiple of 5… )
118 : drill bit angle
55: mitre angle
29: thread angle.
Seeing as it’s for a loupe, those might be the natural cleavage angles for certain gemstones.
I agree. The OP is reading the degrees wrong. It’s 25, 55, and 115.
Nope, it’s definitely 29 and 118 degrees. This site has a depth measuring microscope that includes a “tool reticle” that clearly has those same angles displayed here.
Thanks – yeah – the other image on Amazon was in their app - and the values were more clear - they definitely are what I originally wrote.
Gary T - that was kind of my original guess, but I’ve worked in the jewelery trade (for a small period of time) and never saw anyone using these. Also the angles don’t really match up to stuff like:
Isilder - I saw the drill bit angles were 118 in my WAGS, but that lead to the question as to why is that the angle?
The thread angle is not a bad guess - as one of the reticles also sold is specifically for thread sizes.
Oh wait - I didn’t get that 118 was the angle of the tip - I thought they meant you drilled it in at 118 degrees. I found this tool that also does 60 and 55 degrees:
http://toolmonger.com/wp-content/uploads/2009/02/grinding1.jpg
So I’m guessing it’s probably for measuring drill bits and that 29 is probably important there somewhere too.
I also found another site that sells multiple reticles and refers to this reticle as the “tool reticle” - so I guess that pretty much answers my question - thanks everyone. I never would have guessed sharpening drill bits was the answer and assumed the google result of 118 was a coincidence having to do with some sort of angle/math thing I didn’t understand.