I'd love to be able to estimate what kind of a trip I'm in for, and/or compare my estimated location for the QG with the map to determine if the trip is horse or knarr...
Right now my best estimates are still 10-25 grids off...
------- EDIT FOR CLARITY ------
Okay, a lot of people are answering things aside from the question I'm asking. So let's try this again, now with diagram!

I am asking about the RED arrow, the one that says "THIS ONE" next to it. Note that it points to a bearing marker that shows the way one should travel to reach the quest giver.
In order to triangulate using that, I need to be able to interpret it.
The LAVENDER arrow (pointing up and to the right) is the direction of NORTH.
The BLACK arrow (pointing down and to the right from the character) is the direction of EAST.
Obviously, this particularly quest marker is pointing some flavor of NNE, ENE, or NE, but those are decidedly imprecise. The actual bearing is somewhere between 0 and 90 degrees.
Eyeballing it is no good, because north does NOT point to the top right corner of my screen, it points about two inches down the right side of my monitor instead, so I don't have good reference points. How do I take a more exact bearing from that marker? (I happen to know, because I know that quest giver pretty well, that this particular marker denotes a bearing of roughly 50 degrees, but I want to be able to roughly position and rangefind on quest givers I haven't met yet, where I won't be able to check the map to get an exact bearing as I have done here.)
I know all about triangulation. That's the method I'm using. But that only works with good angles, how do I get the angle from this marker?