What FIX Actually Means
FIX is a specific, technical claim, not a general mood. Understanding exactly what it claims, and exactly where that claim stops, is the foundation everything else in this companion is built on.
FIX means the receiver judges that it has resolved the exact whole number of carrier-phase wavelengths between itself and its reference. It is a statement about the integrity of one geometric calculation, nothing broader.
An Ambiguity, Resolved
A GNSS receiver measures carrier phase with extraordinary precision, down to a small fraction of a wavelength. What it cannot measure directly is how many complete wavelengths lie between the receiver and the satellite. That missing whole number is called the integer ambiguity, and resolving it correctly, for every satellite in view, at the same time, is what a FIX solution actually represents.
Once those integers are correctly resolved, the geometric distance to each satellite becomes known to within a centimeter or two, and the resulting position inherits that same precision. This is a genuinely difficult computational problem, and FIX is the receiver's declaration that it solved it successfully.
The whole numbers behind FIX are not guessed. They are the output of a statistical search and validation process, one that is usually right and occasionally, under the wrong conditions, confidently wrong. That exception is the subject of a later chapter.
What This Claim Does Not Extend To
FIX says nothing about whether the base station's coordinate was surveyed correctly. It says nothing about which reference frame or epoch that coordinate belongs to. It says nothing about whether the antenna height was measured and entered correctly, whether the pole was level, or whether the correction source itself was appropriate for the job. FIX is a precise answer to one specific question, asked and answered entirely inside the receiver's own math.
Why the Word Carries So Much Weight Anyway
Field software reinforces the confidence FIX inspires, usually displaying it in bold green text, sometimes with a satisfying chime. That design choice makes sense: FIX genuinely is the signal a crew is waiting for before collecting a point. The risk is treating that visual and auditory reward as though it answered every other question a trustworthy coordinate needs answered.
FIX represents the receiver's own judgment that carrier-phase integer ambiguities were correctly resolved, producing a precise relative geometric solution. It says nothing about the base coordinate, reference frame, antenna setup, or correction source. Those remain separate questions, answered by separate evidence.
FIX is not the only status a receiver can report. Understanding its less confident sibling, FLOAT, makes clear exactly how much work FIX is actually doing.