Thread:TheRealPella/@comment-26828130-20151126000019/@comment-15636815-20151128074859

Okay, I double-checked the "What links here" page. I didn't see any other templates calling set, either, although those locomotive pages are going to be annoying.

I changed your to  It still didn't work, so I changed it to  That worked. If the template receives no value for parameter  (which it doesn't on the template's own page), then it assigns a default value of 0 and calculates the expression with that. Apparently, if we don't pass a value for a needed parameter, and we haven't specified a default value, then #expr barfs. Now we both know. ;-)
 * 1) expr and #ifexpr don't like raw parameter names. I don't know why.