what you are trying to measure
The same unit as you use to measure any mass. The SI unit for mass is the kilogram.
You use a ruler or tape measure to measure this in units of choice
it is use to measure output
The Unit Used To Measure A Train Can Be Kilometer.
Miles
This depends on what unit you are using to measure in. However, area will always be measure in (unit)^2.
Which unit would you use to measure the water in a full tub?
Feet
to measure a small trashcan
mg
Kilograms
miles