Complex sentence: It comprises a coherent system of units of measurement built on seven base units and a set of twenty prefixes to the unit names and unit symbols that may be used when specifying multiples and fractions of the units.
Split into simpler sentences: It comprises a coherent system of units of measurement built on seven base units. The system also establishes a set of twenty prefixes to the unit names and unit symbols that may be used when specifying multiples and fractions of the units.