Explain what happens if you line up the left side of the object with the 1 on the ruler.

When you line the object up against the ruler you are measuring it's side, if you put it on the one instead of the zero then you're making the object one inch longer, so you'd have to subtract the one in the end

If you line up the ruler with your object at number one. You are adding a cm or in. more and like how they said. You have to subtrat it by one or just line the ruler at the right place