The MyWidth block reports that the width of the turtle is 60 pixels:
If I move the turtle over by 60 pixels, however, the distance is more than the width of the turtle.
Consequently, I realized that I don't understand how the My Width block works, at least with respect to the turtle. What am I missing? (Thanks)
Turtle costume is not a costume and the Laws of Snap! do not apply to it 
Think of it as a singularity
None of the reporters report sensible values (some probably do but best to assume they don't)
Yeah, Jens has this funny idea that the turtle costume isn't a costume, even though everyone says "the turtle costume." But of course it does have a height and width, and Snap! could report them. But I think the idea is that the turtle will be entirely within a 60x60 box regardless of what direction it's facing. So the number isn't altogether arbitrary.
So its the width of the turtle's bounding box, rather than the opaque pixels that form the triangular area. Thanks!
Well, it's the width of a box that's guaranteed to be a superset of the turtle's bounding box. Snap! does know the actual bounding box; it has to, to display it! I'm not sure why we don't report the actual bounding box given the turtle's actual heading, the same as we do for any other costume.