Let's ask the OP if this would've been helpful. Evan, have you read this documentation page? It's available at
Beeeutiful! Only the learner can say if a doc was useful, so ask him :-)
My two cents would be:
Note further that it would be incorrect to replace tt(val) with tt($val) as the latter is affected by the built-in double quote substitution, so that the arithmetic evaluation does not see the name of the variable but rather it's expanded value. Thus if $val = 0, the latter expression would attempt: 0 = 2 + 1 ... which is obviously nonsense. ... maybe too much hand-holding there? ...