Here we are talking about the measurements. The measurements has 4 parts: condition, magnitude, uncertainty, and label. 
	WHAT?

 Please have patience. If I say I 40. You may ask what 40. Ami 40 years Old or I ran 40 miles or I jumped 40 miles. To define a measurement, you may have to explain the condition.

Now if I say I ran 20, this explains the condition, but doesn't mention the units or the magnitude. So I must say that I ran 20 miles /hour.

Again a cheetah can run up to 60 mph. If I have to compare my speed with a cheetah's speed, there wouldn't be any unit after the value. A label explains the units of measurements. When it is a ratio you must compare the same unit type like meters with meters or hours with hours. You can't compare meters with hours. 
 

In the example above, we are converting one unit to another. The similar unit labels (inch) are canceled out.