I've tried using the rating scale guidelines, but some things just don't seem to fit. There is nothing in there about how to rate one when you put it in a tree. For terrain, it talks about slopes and whether you could ride a bicycle or push it. I've seen ratings where it's a 1.5/3 because the cache is up a tree, yet the walk to the tree is a breeze. To me, that rating is backwards because the difficulty isn't the journey there, the hard part is actually getting the cache. That's more of a puzzle. How to get it down from the tree.
OTOH, a terrain 3.5 or 4 tells me I have to CLIMB the tree (or arch, or whathaveyou)
Many of those hides are easy to spot from below (even whilst backflipping off a median planter), therefore justifiably only 1.5s or 2s.
I could use a lot of things to simplify any tough terrain, but they all have hints -- subjective as they may be -- to where to be looking for the cache.
And, well, to get a bike into a tree, that's a BIG push!!!!
So. Rule of thumb when *I* am setting ratings:
Difficulty - trickiness of the hide. If it's a straightforward hide atop a lamppost, it's still a 1. If it's an electric plate flush against the top of that lamppost, it's a 4... or a bolt in the top of that lampost, maybe even a 5 Terrain -- 1 -- wheelchair access. We learned a lot about this when Semper Q was on wheels. Not only does the chair have to get to GZ, but the person in the chair has to reach/retrieve the cache from that chair (e.g. NOT on the ground). So most simple caches are really 1.5s, we learned. And on from there. 4 means a tough climb (whether up someone's shoulders or whatever). 5 means it requires special gear. For example, Spring Loaded for Waterweasel & I was probably a 3 as far as exertion -- but because it needed fins and mask/goggles (if not snorkle) to do realistically, it's a 5. Hubbard Glacier Earthcache. We viewed it from the veranda of our stateroom. Hardly any physical effort at all. But because it required a boat or a helecopter, it's a 5 Terrain.
Yes, for some a 4 or 5 terrain is a lot easier than for others. For some a 3 terrain is next to impossible. So you also need to know the Cache Owner's prejudice & capability. OTOH, these ratings tell this cacher quite a lot about what to expect and how to look for the cache. Even though they're all over the place. Well, for that matter, so are cache sizes. These days I'm seeing smalls regularly classified as regulars and a waterproof match case or altoids tin (micros when we started), as smalls. Suppose we need Micro, Mini Micro, and You have GOT to be kidding/How did you get a LOG in there?!?
This is all my subjective take, based on how I've learned to play (and thus calibrate) the game. So there are certain people like TreyB & the Outlaw who are likely to blame for my point of view. LOL.
To me, difficulty is how hard is it to FIND the cache once you arrive and terrain is how hard is it to GET TO the cache location.
In the tree example, yes, the walk to the cache was probably a 1-1.5, but that last little bit raises the difficulty. When you arrived at ground zero, the cache was in a mostly obvious hiding place, so it warrants a low difficulty rating.
If that was my hide, I'd probably mention something in the description that I rated it a 3 overall, but only because the last bit of terrain will make retrieving the cache harder than the walk there.