The Permanent Service for Mean Sea Level, housed within the Institute of Oceanographic Sciences at Bidston on Merseyside, is charged with task of collating mean sea level data from all known tide gauge stations on a worldwide scale. This information has been published in a number of volumes, the first of which appeared in 1940. By the late 1960s several of the earlier publications were out of print, and the opportunity was taken to review the entire method of data publication.
The most serious single criticism of the original system stemmed from the common practice of relating sea level to a national fundamental reference point remote from the station. The difficulties of transferring levels across great distances with high precision are well known, and in consequence the problems of geodesy become confused with those of oceanography. The recommendation therefore was to strive to achieve homogeneous data series in which the datum for sea level at a station is referred to a local Tide Gauge Bench Mark and to ensure that this relationship is maintained. In this way the movements of sea level with respect to the bench mark on the one hand and the repeated definition of the height of that bench mark within a leveling network on the other hand became the responsibility of separate disciplines. On this basis it was agreed that the total mean sea level data bank should be reviewed, revised, and republished.