Tidal diamond

The symbols consist of a letter of the ISO basic Latin alphabet in a rhombus, printed in purple ink.

[b] On any particular chart each tidal diamond will have a unique letter starting from "A" and continuing alphabetically.

[1] Either somewhere on the chart (generally on land) or else on a separate sheet, will be a Tidal Diamond table.

For instance the row for 3 hours after high water is valid from HW+2½ to HW+3½, not from HW+3 to HW+4.

To calculate the rate at an intermediate tide between neap and spring, interpolation is required.