Answer:
to support commerce
Step-by-step explanation:
Units of length, mass (weight), and time are defined as national and international standards in order to support commerce.
When you go to purchase a given length of material, you can only do that if your unit of length is the same as the merchant's unit of length.
The same is true for a mass of material. You can only be assured of obtaining 10 pounds of apples, if your pound is the same as the merchant's pound.
If you contract your time at some rate per hour, you and your employer will only be satisfied if your time units are the same.
That is, standard units of length, mass, and time are required for orderly conduct of business.
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Additional comment
The SI system of units defines the meter, kilogram, and second using specific numbers of wavelengths of light. These are presumed to be immutable properties of the universe. (We're not so sure anymore.)
