Prior to 1970 data supplied by N.O.A.A.
=========================== FOLLOWING PSMSL DOCUMENTATION ADDED 11-Jun-1991
San Juan            848/041 RLR(1964) is 10.8m below BM1
=========================== FOLLOWING PSMSL DOCUMENTATION ADDED 12-Jul-1993
Evidence for a datum shift either side of a data gap in the mid 1960s.