The temperature to be observed is that of the sea surface representative of conditions in the
near-surface mixing layer underlying the ocean skin.
The sea-surface temperature should be very carefully observed. This is because, amongst
other things, it is used to obtain the difference with air temperature, which provides a measure
of the stratification of temperature and humidity and of other characteristics of the lower layers
of maritime air masses. For these reasons the temperature of a seawater thermometer should
be read to 0.1 °C.