At some USGS stream-gage installations, NOAA’s National Weather Service (NWS) maintains a separate stage sensor that is serviced by NWS technicians. Calibration of any sensing device can occasionally drift from a "true" value, so there might be differences between USGS and NWS data reports.
USGS personnel visit installations on an interval of 6 weeks or less to maintain equipment and make required adjustments. NWS technicians have a separate maintenance schedule. In either case, data retrieved from remote sensors is always considered provisional and subject to revision after quality control and analysis. Differences between remotely reported and field-measured data are usually small and within tolerances required for water resources management and control.
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