Editing VHF omnidirectional range (section)

===Testing===
Before using a VOR indicator for the first time, it can be tested and calibrated at an airport with a ''VOR test facility'', or VOT. A VOT differs from a VOR in that it replaces the variable directional signal with another omnidirectional signal, in a sense transmitting a 360° radial in all directions. The NAV receiver is tuned to the VOT frequency, then the OBS is rotated until the needle is centred. If the indicator reads within four degrees of 000 with the FROM flag visible or 180 with the TO flag visible, it is considered usable for navigation. The FAA requires testing and calibration of a VOR indicator no more than 30 days before any flight under IFR.<ref name="VOT">{{Cite web
|title = VOR Navigation
|last = Wood
|first = Charles
|year = 2008
|url = http://www.navfltsm.addr.com/vor-nav.htm
|access-date = January 9, 2010
|archive-date = October 11, 2007
|archive-url = https://web.archive.org/web/20071011051729/http://www.navfltsm.addr.com/vor-nav.htm
|url-status = live
}}</ref>