A prototype tide gauge having an accuracy of

% of the tidal range and a resolution of

% suitable for unattended use over one year is described. It is based on an Aanderaa data logger and a differential pressure transducer installed together on the sea bed; tidal data is recorded internally, digitally at half hour intervals. A cable containing electrical conductors and a kerosene-filled hose rises to the shore allowing air pressure to be sampled, calibration to be checked, and telemetering/ transponding equipment to be attached. The instrument has been in limited commercial production; the first unit was installed at 80

N. during August, 1972.