Q. Why do you obey a plank of wood?A. Because it’s a ruler.

My father’s jokes aren’t always the most sophisticated, but I was reminded of this particular witicism when buying a wooden ruler for Smudge recently.

Not just any old wooden ruler, you understand. Oh no! See, one of its sides lists kings and queens, with the dates of their reigns.

And that makes it interesting. For Smudge will face a little test the next time I visit her at University, with the questions drawn from the very implement that will thwack her oustretched palms should she get her answers wrong…