Thus, the Span field in the Quality Assessment may not match the span of the distribution data set. As the questionable datum shifts are resolved, the data set will be updated. Although this policy adds some complexity, it allows more rapid dissemination of at least the quality assured years.
For each year, the following information is documented from the quality-controlled hourly data with dates given as the nth day of the year starting from 1 January:
1) a Completeness Index (CI) based on the percentage of hours with available data,
2) a list of gaps longer than a day,
3) a summary of days with consecutive missing or obviously wrong data in a time span longer than 6 but less than 25 hours that have been replaced, with hours in parentheses, and
4) a summary of days with questionable fluctuations in the residual series. Fluctuations within the residuals are considered significant and are noted if they are greater than 25 cm. This policy has changed slightly as of October 1992: only suspicious fluctuations due to obvious instrumentation problems are noted. Minor timing drifts are no longer included in the list of questionable days.
Note: If the predicted tides poorly model the observed heights due to the inability of the tidal analysis to completely resolve the non-linear shallow water effects, the residuals are not suitable for assessing the data quality. Instead, a subjective comment on the quality of the data is provided.