1. A method for obtaining a true azimuth heading for correcting a coarse azimuth heading measured from an observation position to a specific selected target by operating a data acquisition system disposed at the observation position, comprising: a computer module running computer programs including at least one dedicated computer program and at least one map, a computer display coupled to the computer module for: displaying output data to the operator in superimposition onto the at least one map, and for responding to an operator input designating a selected location thereon by operation of the computer module for: retrieval of location data of the selected location, and replacement of location data for a previously calculated location with location data of the selected location, a sighting device aimed at the specific selected target and coupled to the computer module for input therein of data including location data and target data, the sighting device including: access to a source of location data, devices for measuring target data, including elevation angle, relative horizontal yaw angle, coarse azimuth heading, and means for deriving range data, the method comprising the steps of: feeding input data into the computer module including location data, target data and associated errors limits, and operating the computer module for: displaying the at least one map selected according to observation position location data, running the at least one dedicated computer program to provide calculated target location data for the specific selected target according to input data, and to calculate an error area delimited by data error limits and displayed as a search zone, the calculated target location being disposed within the search zone containing the specific selected target, and superimposing the search zone on the at least one displayed map, prompting the operator to search within the search zone limits shown on the display module for the true location of the specific selected target, which when found and indicated, operates the computer module for: retrieval of location data of the specific selected target, and replacement of location data of the previously calculated target location with the true location data of the specific selected target, and operating the at least one dedicated computer program to calculate and accept the sighting device's heading aimed at the specific selected target as the true azimuth, to feedback the true azimuth to the sighting device, and to display calculation result data, whereby the data acquisition system provides true azimuth from which a true North direction may be derived and used as input for further operation.