I’m shaping the arch on my cello. As with drawing, I have a little problem where I have my face is right up against the workpiece. It’s always good to step back and get a macro reading of the shadows to judge where to scrape next. On cello this is harder to do at your desk unless you have extendable arms (which I unfortunately do not).
Fortunately there is a very bright light (the sun) and a mirror (our front door) outside. Everyone passing by on Oakton at 5:30pm today would have seen me holding my cello plate up to the school, Simba-style.
I love the hard shadows from the sun.
Keep the centerline of the plate at the same angle of the sun for a very unforgiving reading of arch symmetry (looks like I still have a little work to do):
fix it with shading 
“Simba Style* ” Its the Circle of Liiife”….
“But don’t we eat the antelope?” “Yes, but when we die, our bodies become the earth, and trees grow out of the earth. And then people chop down the trees and turn them into violins. Then the violins get destroyed and turn into dirt and grass grows out of the dirt and the antelope eat the grass. And so we’re all connected in the great circle of life.”