There's a 'should' either stated or implied.
Some confusion in that:
In economics “Normative Econ” often means axiom based approach. State “reasonable conditions on preferences and production functions” derive necessary implications. See… most of books like Mas Colell et al.
In common parlance, maybe in psych, I’ve hear “normative behaviour” used to mean something like “typical, normal, socially acceptable behaviour”
I don't think there's a perfect answer, but as a heuristic I defer to the logical positivists - if you can't even in principle find direct evidence for or against the statement by observing the physical world and you can't mathematically prove it, and on top of that it sounds like a statement about behaviour or action, then you're probably in normland.
Why is it not considered normative? It follows rules of arithmetic. The operation should be carried out according to "correct" procedure and failure to do so results in something "wrong". So why no count as normative?