Basically what's documented here: What formula should be used to determine "hot" questions? We have a few tweaks: Succeeding questions from the same site are penalized by increasing amounts. So, the first question from SO in the list gets multiplied by 1.0, the second by 0.98, the third ...

Because you used \rm instead of \mathrm. \rm is not a macro which accepts an argument, as you apparently thought. The macro which does that is \textrm{text} for text mode and \mathrm{text} for math mode. Instead, macro \rm changes the current font to roman, from the point in which the macro appe...