A successful request is not the same thing as a current observation.
There are two clocks
The observation time tells you when the source recorded a value. The retrieval time tells you when BoatWaypoint received the response. Reloading a page can change the retrieval time without producing a newer measurement. Read both timestamps with their time-zone labels. A fresh page render should never be mistaken for evidence that the underlying sensor has just updated.
The current BoatWaypoint rule
For the air-gap flow, this version requests a bounded 72-hour observation range and uses the newest valid returned point. A point no more than 18 minutes old is labelled live; older returned points are labelled stale historical context. This is a display and data-handling rule, not a certification that an 18-minute-old value is adequate for a particular manoeuvre. The methodology page documents the same boundary.
Worked example: a recently retrieved old value
Suppose the response is retrieved at 12:10 UTC but the measurement is stamped 10:00 UTC. The measurement is 130 minutes old, not zero minutes old. Even if the historical arithmetic produces a positive margin, that result must not be treated as the current overhead gap. The stale label qualifies the entire comparison, not just a small source footnote. All times and values here are illustrative.
Unavailable is not a numerical result
A station may return no observation in the requested range, or the upstream request may fail. In either case, no present clearance can be inferred from the absence. Keep the official station link and try an appropriate authoritative check instead of substituting zero, the last number you remember or a neighbouring sensor. The browser may still report that the request is complete; that describes the request lifecycle, not the availability of a usable measurement.
Keep saved planning notes honest
A printed checklist is a record of what you checked, not a live instrument. Recheck source conditions before relying on an earlier note, and keep the original measurement time rather than silently replacing it with the printing time. Mark unresolved data explicitly. This principle also applies to chart metadata and operating restrictions: a date attached to one source does not prove that every other dependency has been checked for your intended passage.
Inspect an observation and its timestamp
Keep the inputs, source references and unresolved dependencies together.
Inspect an observation and its timestamp