How I measure the gap in my teeth.

Dad gave me this calliper set. It is lots of thin slivers of metal. For ages I could fit the whole set into the gap, which means it was more than 2mm, but now I fold one back (one that is 25/1000 of an inch) so I can tell that the gap is smaller, and the set I can fit in is a bit over 1.5mm wide.

This is a lot more accurate than putting a ruler in my mouth.