This is a helping tool for when you are painting something that
has a lot of detail that you may not be seeing too clearly, even
though it is right there in front of you. Take a photograph,
a close-up of the detail and study that.
I did this recently for a student who was having trouble seeing
the way the lines of the pattern curved around. With the
photograph that you see above, it became much easier to see
what was actually happening. And she drew it correctly!