Good post at PANBO about chart depths Zones of Confidence or ZOC
NOAA introduces Zones of Confidence; mind your ZOC
Categories of Zones of Confidence (CATZOC)
CATZOC allows a hydrographic authority to encode data against five categories (ZOC A1, A2, B, C, D) with a sixth category (U) for data which has not been assessed. The categorisation of hydrographic data is based on three factors (position accuracy, depth accuracy and seafloor coverage), as specified in IHO publication S-57.