The invention relates to a method for adjustment of a harmonization compensation applied to alleviate a discrepancy of conformity between a video image transmitted by a video transducer (1) and projected by a head-up display device (5, 6), of an aircraft, and an external scene ahead of the aircraft. At least one equipment item of the aircraft—preferably the said HUD device—equipped with at least one control element accessible in the cockpit, is programmed to be able to function according to a nominal mode and according to a maintenance mode, in which at least one of its control elements, known as a redirected control element, is used to define the applied harmonization compensation. An operator activates the maintenance mode and starts an adjustment operation, in which he modifies in real time the applied harmonization compensation, by manipulating at least one redirected control element, until the video image is matched with the external scene.