[axqqhovx] Digits as shades of gray

• 0 = 000
• 1 = 001
• 2 = 002
• 3 = 011
• 4 = 012
• 5 = 022
• 6 = 111
• 7 = 112
• 8 = 122
• 9 = 222

Three concentric rings (innermost one is a disc), like a bullseye target, that are colored 0=white, 1=gray, 2=black, assuming a white background.  The three digits left to right correspond to the color of the rings from outermost to center.  Unlike a bullseye target, colors don't alternate.  For every digit, the rings go from light to dark, outermost to center.

The structure is 1 + 2 + 3 + 4 = 10.  Previously on how the appearance of a digit ought to encode its value.

Perhaps a fourth outermost ring that is always present, so zero does not look like space, and in fact looks like regular zero.