The world's smallest playable guitar is 13 micrometer long. Express the length in standard form.

Though meter (m) is the basic unit of length as per SI
units, use of multiples and subdivisions of meter is also permitted in the SI system.
Different standard practices are used by people in different profession. For measurement
of small lengths such as a guitar that is just 13 micrometers, some alternative standard
representation of its length will be:

• 13
  micrometers


• 13x10^-6
  meters


• 13x10^-6 m


• 0.013
  millimeters


• 0.013
  mm

An engineer will perhaps describe this
length as 13 microns.