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Category Zones of Confidence indicates the accuracy of the hydrographic data on the chart. The CATZOC table shows the position accuracy, depth accuracy and survey quality of each ZOC value. A misconception is that buoys, drilling rigs and other obstacles are indicated with the same accuracy as the position accuracy in the ZOC table. The accuracy of these objects depends on data provided by third parties to the UK Hydrographic Office. Mistakes regularly creep in. A common inaccuracy is that mistakes are made with degrees, minutes, seconds and degrees, minutes and tenths of minutes.

The Disciplinary Court wishes to point out that any seafarer who observes a position error of a drilling platform or any other object can report this to the UK Hydrographic Office by means of a Hydrographic Note (see NP 100, there is even a separate app developed for this: the Admiralty H-Note; this can be downloaded from the IOS and Android App store).