Currently, the US officially uses the Imperial (or standard) unit of mesurements for most things. There is a growing movement to convert to the metric system, but has not caught on with a whole lot of support. The US does use metric for some things. An example would be we use 1 and 2 liter bottles.
the units mersured in astronomy astronomers use lite years the distance that lite travells in a year is trillion miles
SI units is what we use in the United States for the common unit of measurement for matter.
Length
meters.
length / distance
Units of length:femtometerangstrommillimetercentimetermeterkilometermil (thousandths of an inch)inchesfeetyardfathom
Units of measurement provide a standard to measure mass, length etc.So, it is useful.
Units of measurement of length.
Units of measurement of length.
It could be if you wished to use near-obsolete measurement units.
A ruler would work best if you are wanting to measure the length of an eye dropper.
Units of measurement are useful to rationally measure anything.
mass, length and time are the basic measurement units