Why do we need a Standard Measure?

In math today we did an exploration to measure our classroom's width.  We used students to see how many "second graders long" our room was.  Students quickly realized that this was not a very accurate way to measure.  They pointed out many reasons it wouldn't be a measure that would make sense to anyone but us.  They understood that our classmates come in many sizes and this alone would change the results every time we measured.  Tomorrow we will get busy with yardsticks and meter sticks.  Let the accurate measuring begin!