The -901 means the data value is missing.
This can happen due to remote gage mechanical malfunction or interrupted data transfers. The -901 value can also be placed in the data set by Water Management's data quality checking programs or the database manager. Our data are checked for specific quality characteristics automatically every hour and verified manually once a day.

Quality Characteristics Tested:

• Absolute Magnitude

• Duration Magnitude

• Rate of Change

• Constant Value

The -902 number means the data value is invalid.
If an incoming data value fails a quality check, the value sent is replaced by a -902 value. The database manager can then decide to change the value to a -901 (missing value) or replace the bad value with an accurate data value.