Final answer:
One millimeter (mm) is equal to 1000 micrometers (um) in the metric system, which is based on powers of ten.
Step-by-step explanation:
A millimeter (mm) is a unit of length in the metric system, which is widely used for scientific measurements. One millimeter is equal to 1000 micrometers (um). The factor of 1000 is used because the metric system is based on powers of ten, and there are 1000 micrometers in a millimeter because 'micro-' denotes one millionth while 'milli-' denotes one thousandth. Thus, when converting from millimeters to micrometers, you multiply by 1000.
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