| Term | Definition |

| Calibration Value | A value used as part of the calibration of an instrument at a particular time. |

| Derived Value | Data are the result of a mathematical transformation where there is some subjectivity in the selected equation form and/or where parameters are typically fitted. A rating curve relating stage to discharge is a transformation that fits this definition; therefore stage is observed but discharge is derived. |

| Estimated Value | Values that are roughly calculated, judged, or approximated. Values may result from professional judgement or from ancillary data. |

| Field Observation | Data reflect the measurement the sensor is designed to make, reported at the frequency of data collection |

| Model Simulation Result | Values generated by a simulation model |

| Sample | Observation that is the result of analyzing a sample in a laboratory |

| Unknown | The value type is unknown |