# Meter

A meter is the SI unit of distance. The meter is defined as the length of the path travelled by light in vacuum during a time interval of 1/299 792 458 of a second.[1] The meter is defined as a measure of time because time can be measured far more accurately than length (at the time of the definition, time could be measured up to 1 part in 1013 whereas length could only be measured up to 4 parts in 109).[2]

Metric prefixes make longer units like kilometer, km (1000 m) and megameter, Mm (106 m) and smaller units as well like millimeter, mm (0.001 m) and the μm (10-6 m). The μm is called both the micrometer and the micron. The word micrometer is ambiguous since it's also a device that measures very precise lengths, hence the two terms.

## For Further Reading

Read more about meters Dr. Rowlett's unit dictionary.

## References

1. NIST. Historical context of the SI [Online]. Available: http://physics.nist.gov/cuu/Units/meter.html
2. New Scientist. (1963). Time to remeasure the metre [Online]. Available: http://books.google.ca/books?id=pKU5MXqo4UYC&pg=PA258&redir_esc=y#v=onepage&q&f=false