Some have special names, like frequency, force, and flux density. There are some units in popular or professional use, which are outside this system. In this course, non standard units should be automatically converted before use. The full table is shown, but usually only the prefixes between Tera and pico are used. Ternary form uses only the prefixes above and is the preferred form for this course.
Significant figures give the number of digits which establish the accuracy of the measurement.
For example, if the average radius of the Earth is given as 6360 km, this implies that the measurement is meaningful only to 10s of km. Calculators give all the digits they can display, so calculator results should have the number of digits reduced to show the accuracy of the result.