What Does a Sensor Quality Flag Represent?
From the earlier reference collection. Read the current software blog.
A quality flag is useful only when its meaning and effect on display, inclusion, and interpretation are documented.
A flag is a label with a contract
A quality flag attaches a status to a record or value. Its meaning depends on the system that defines it: “review,” “suspect,” or a numeric code may indicate very different conditions in different feeds. Readers should not have to guess whether a flag signals a confirmed error, a possible issue, missing metadata, or simply a review workflow.
Publish a legend that gives each flag a stable name and plain-language definition. If a flag comes from a data provider, preserve the provider’s meaning rather than silently translating it into a stronger claim. A local tool may add its own status, but it should distinguish that status from the source’s flag.
Explain operational effects
The definition should say what happens when a record receives the flag. Does the value remain visible? Is it omitted from a default chart? Does it still enter an average or download? These choices affect interpretation and should be discoverable beside the data, not hidden in implementation details.
For instance, a “provisional” value might remain on a graph with a marker and be included in a download, while excluded from a finalized summary. Another tool might include it everywhere but show a warning. Either design can be coherent if it is documented and applied consistently.
Keep flags from becoming verdicts
A warning does not always mean a reading is unusable. A sudden change may be a real event, and a maintenance-related flag may tell the reader to consider a break in comparability rather than discard all observations. Conversely, an unflagged record is not a guarantee that every aspect of measurement is correct.
Separate the flag itself from a later decision to include or exclude a record. Preserve the raw value, record when the flag was set, and retain the basis for any review outcome. This gives analysts room to apply different criteria without losing the original context.
Make the explanation practical
A useful interface can show the flag’s short label, a hover or details explanation, and a link to the relevant source documentation when one exists. In a download, include a readable flag field or a companion data dictionary so the status survives export.
A flag should guide a reader toward the right questions. Define it clearly, explain its consequences, and leave room for evidence that does not fit a simple pass-or-fail label.