I was reminded of this article by Michelle Francl[cite]10.1038/nchem.1733[/cite], where she poses the question “What anchor values would most benefit students as they seek to hone their chemical intuition?” She gives as common examples: room temperature is 298.17K (actually 300K, but perhaps her climate is warmer than that of the UK!), the length of a carbon-carbon single bond, the atomic masses of the more common elements.