These data represent inferred sea level from a sub- surface pressure gauge, which measures the combined weight of the column of water and air above it. A constant atmospheric pressure has been subtracted, but variations in atmospheric pressure, which would not be sensed by a conventional float/ well gauge, would affect the measurement of the sub-surface pressure gauge. The depth of the instrument in the water is unconfirmed.
O.R.S.T.R.O.M. Lop Museum 43-45 Rue Cuvier 75231 Paris CEDEX 05