1) metre ruler is inapproriate to measure the length of classroom. It must be measuring tape Because it have long metre and approriate for the long lenght like the classroom compared the metre ruler for the length of the table, cloth and so on .
2)a strand of hair is to short to use the metre ruler so far. Why dont we use the micrometer or the real name is micrometer screw gauge to measure the thickness of a strand of hair. It approriate to measure the thickness like paper, or something like u ask a strand of hair like that.
Psss: this my opinion and i hope will help you even a piece?? Emm okey , nice to help u then :))