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ruler; measure
先生が物指しを使って黒板に線を引いた。
The teacher drew a line on the blackboard using a ruler.
物指しが見つからなくて手で長さを測った。
I couldn't find a ruler, so I measured the length by hand.
自分の物指しで他人を測ってはいけない。
You shouldn't measure others by your own yardstick.