I was in Grade 3, I think.
The ruler was a wooden Rulex Trueline, an object that will be familiar to anyone in Australian education in the 1960s.
It took me months to eat but I was determined. Towards the end, I had to get a new Rulex Trueline in order to rule lines of sufficient length to pass muster for margins, double underlinings and equilateral triangles.
I’m not particularly proud of the achievement but, as far as I know, It is unique.
Here’s a Rulex Trueline . If I hadn’t eaten it, it appears that it would now be an antique.