This data set contains CTD data collected during the DAUNE experiment using the given sensor. The goal of this experiment was to reach a common understanding of how measurement uncertainty can be derived initially focusing on temperature data. Data collection was performed using the AWI O2A infrastructure (https://epic.awi.de/id/eprint/37171/) which performs automatized near real time quality control. During the data ingest and archival process, the hereby assigned quality flags used by the O2A system have been transformed into the pangaea flagging scheme as follows, flagging symbols are shown in brackets: O2A Flag ->PANGAEA FlagNo quality control (0) ->unknown (*)Good data (1) ->valid ()Probably good (2) ->questionable (?)Probably bad (3) ->questionable (?)Bad (4) ->not valid (/)