|From Ocean Navigator #90
Furthermore, an offset can be entered manually by the operator to take care of datum shift problems such as the one Mr. Calder mentioned.
I note that the chart in question was compiled after 1975, at which time WGS 72 was the standard. There is no significant difference between the WGS 72 and WGS 84 datums. If the cartographer knows how much to shift GPS positions to agree with the chart, he knows how much to shift the lat/long grid to match the GPS, and hopefully will do so in future editions.