Notes:

- Inner loop, or concavity.
- Concavity.
- Ambiguous top edge – Curved or flat.
- Possible left-hand edge.
- Lower curvature.

A 0 requires a curved
top and a curved bottom, and either convex or straight left and right
edges. There is minimal support for these features in symbol #18. This
excludes a 0.

A 1 needs a narrow
width, horizontal top. There is no support for this as symbol #18 has
a wide curved top. A 1 needs long vertical edges. There is no support
for this in symbol #18. This excludes a 1.

A 2 requires a short
edge to the top left, top curvature, and a diagonal from the lower-left
to the upper right, and a wide flat bottom. There is minimal support for
these features. This excludes a 2.

A 3 requires a short
edge to the top left, a concavity on the right-hand edge, and lower curvature.
There is minimal support for these features in symbol #18. This excludes
a 3.

A 4 needs a left-hand
vertical edge, or a diagonal from the middle-left to the upper right,
and a vertical right-edge. There is no support for any of these features.
This excludes a 4.

A 7 needs a wide
horizontal top, and a diagonal from the lower left to the upper right,
and a narrow foot in the lower-left. There is no support for 2 of these
features. This excludes a 7.

An 8 requires a closed
loop on both the top and the bottom (requires upper and lower curvature,
and left and right concavities). Symbol #18 has minimal support for these
features. This excludes an 8.

A 9 requires a closed
loop on the top. A 9 also requires a diagonal line from the lower-left
to the upper right, and a narrow, horizontal foot. There is minimal support
for this in symbol #18. This excludes a 9.

A 5 needs a wide
horizontal top, a top-left corner, and a short left-hand vertical edge
from the top, and lower curvature. Symbol #18 supports these features.

A 6 requires a left-hand
straight vertical edge, or convex edge. A 6 requires a lower loop with
lower curvature, and a right-edge concavity. Note number 4 points out
a small vertical section which may differentiate the symbol as a 6 vs.
a 5.