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running Fix A position determined by crossing lines of position (LOPs) obtained at different times that are then advanced or retired to a common time. Unless your vessel is completely stopped, all fixes are running fixes since you move off of the first sight immediately after taking it. Sometimes sights taken within a few minutes of each other are not considered a running fix when the errors in neglecting the motion of the vessel are not significant. For the most accurate work, however, even small motions should be corrected for. The accuracy of a running fix, is dependent on how well you know your motion between the two sights, which is your CMG and SMG. To know these you must have calibrated log and compass, and you must know what the current is, if there is any. When you know all of this, then a running fix is as good as a stationary fix using two different targets. A special case is when the first LOP is parallel to your course line, such as a cel nav sight taken on the beam or a bearing or range line taken dead ahead or astern. With no current present, this first line does not change, so your second sight is an accurate fix without corrections. Since all fixes are in effect running fixes, it is always best to choose the first LOP as the one that is changing least with time. Moving the first LOP to the second is called Advancing an LOP. Moving the second back to the time of the first is called retiring an LOP. Abbreviation:  rfix

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