Hal as accomplice; the Weston house (p. 952)
As in all the subdorm rooms and hallways, a guilloche ran around our walls half a meter from the ceiling. New E.T.A.s always drove themselves bats counting their room's guilloche's interwoven circles. Our room had 811 and truncated bits of -12 and -13, two left halves stuck like open parentheses up in the southwest corner.
Context
E.T.A.'s buildings are banded with a guilloche — interwoven circles running around every room — and new students obsessively count them. Hal knows his room holds 811 and two halves. The academy literally lives inside rings, and the kids can't stop tallying them.