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Term |
Definition/Description |
Source |

X.25 |
Recommendations developed by CCITT [now ITU-T] that define a protocol for communication between packet-switched public data networks and user devices in the packet-switched mode. | TAFIM 3.0 |

X.400 |
The international standard developed by CCITT [now ITU-T] for a store-and-forward message handling system in a multivendor environment. | TAFIM 3.0 |

X.500 |
The international standard protocol developed by CCITT [now ITU-T] for directory services for electronic mail. [DISA/DO3 (CIO)] | DISA CFS |

X/Open Company Ltd. |
Now called The Open Group. |
Open Group Web Site |

x-axis |
1. (JCS) A horizontal axis in a system of rectangular coordinates; that line on which distances to the right or left (east or west) of the reference line are marked, especially on a map, chart, or graph. 2. The line joining the opposite fiducial marks in the direction which is most nearly parallel to the line of flight. |
HDBK-850 |

x-coordinate |
See abscissa. |
HDBK-850 |

x-coordinate |
The x value, abscissas, coordinate of a point in a plane Cartesian system obtained by measuring parallel to the x-axis. | ISO/TC 211 |

x-correction |
The correction to an x-direction. | HDBK-850 |

x-direction |
An observed direction in a triangulation figure for which an approximate value is obtained and treated like an observed direction in the adjustment of the figure. The work of a least squares adjustment of a triangulation figure sometimes requires the use of an x-direction, for which an approximate value is obtained by an inverse position computation, by the solution of the three-point problem, or by other means, and then using the x-direction in the adjustment and obtaining a correction (x-correction) for it, which makes it consistent with the adjusted values of the observed directions. | HDBK-850 |

x-displacement |
A component of image displacement. When a point image is to be located by coordinates with respect to rectangular axes, x-displacement represents the distance moved in the x-direction. | HDBK-850 |

x-motion |
In a stereoplotting instrument, that linear adjustment approximately parallel to a line connecting two projector stations; the path of this adjustment is, in effect, coincident with the flight line between the two relevant exposure stations. | HDBK-850 |

x-parallax |
See absolute stereoscopic arallax. |
HDBK-850 |

x-scale |
(JCS) On an oblique photograph, the scale along a line parallel to the true horizon. |
HDBK-850 |

x-tilt |
The component of tilt about the x-axis, which is most nearly in the direction of flight. Also called list. |
HDBK-850 |

x-y scaler |
An instrument that provides x- and y-coordinates in digital form from analog data. | HDBK-850 |

*Last Updated by Mark Owens 17 February 1999.*