How did defining an inch with barley grains have both pros and cons?

[frozen7]

Long ago in england, the inch was defined as the lengthof three barley grains placed end to end. In what ways was this a good way to define a standard? In what ways was this a poor way to define a standard?

Does anyone know how to answer this question?

 

[HallsofIvy]

Yes- you answer it by THINKING! I doubt that there is any good way to help you here short of giving you the answer- and that isn't the point of the question. Think about what you need to have a "standard" measure.

 

[frozen7]

Is it because all barley are similar in size?
and it could be a bad way since not all barley same in size actually?

 

[HallsofIvy]

That's a good start! Now what other reasons can you come up with?

 

[Jameson]

Consider that fact that some things are common and easy to visualize. For instance, I live in America so I can visualize a mile. I have grown up with it as a standard unit of measure. But ask me to run a kilometer and I'm stuck. With someone common measurements can have more meaning as more people understand them.

As for the cons, you have a good start. Exactness is the key.