Permanent Vertical Control. To establish an accurate datum for vertical control would involve tidal observations over an extensive period. It is re= commended that such observations be taken in cooperation with the U.S. Coast and Geodetic Survey. This consists of setting up an automatic tide gauge if one is not in operation at the Atoll, and a periodical servicing of this instrument. I1t is believed that the Coast and Geodetic Survey would install the gauge and that operation of it would require very little time of this organization. The Los Angeles office of the U.S. Coast and Geodetic Survey states that a project is under way to establish a datum for vertical control throughout the Pacific Island areas, This operation is reported to be in conjunction with the U.S. Army and will extend over a four-year period. It is believed that more definite information can be obtained from the Honolulu office of the U. S. Coast and Geodetic Survey. It is recommended that the U.S. Coast and Geodetic Survey be advised that further tidal and current data are of interest to the AEC project, and that the U. S. Coast and Geodetic Survey be requested to make iniwetok an observation point in any scheme of vertical control planned for North Pacific areas. Tidal Datum. The tidal datum used for this area is Mean Low Water Springs, which may be defined as the mean of the low waters of the spring tides which occur within a day or two after the moon is new or full. Tide predictions are obtained from the U.S. Coast and Geodetic Survey pub- lication, "Tide Tables of the Pacific and Indian Oceans", and includes the following data for 1949 at Eniwetok Atoll: Mean range Spring range 267 3.9 Lowest low tide Oel Highest high tide 5.3