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Diagram for determining the tides

The scheme is as a kind of compass arranged around with the initials of the winds. The orientation of these characters invites us to return it, north and down. The lunar disc in which fits a face oriented towards the West is in the southern direction, ie the upper meridian passage which, at the new moon occurs at 12 h. On this 24-hour clock, the letters P and B indicate the time and day of the new moon, respectively, of high and low waters for 14 sites; the letters P and B cut into 4 quadrants of 6 h, the circle corresponding to each site. These are distributed Sein Island at the mouth of the Seine and not of Gibraltar to the Pointe de Penmarch legend as we announced.

The moon makes its daily journey in 24 hours and 50 minutes; knowing that the new moon passes the meridian at 12 pm; 2, 3, n days later, the moon pass the meridian to 12 hours. most 2, 3, n times 50 min; the same offset, added to the hours designated by the letters B or P give time low and high tides. For example, the fifth day of the moon, to the island of Batz, tides reversals will occur with a lag of 4 h 10 min (50 min x 5) with respect to the hours given by the letters P and B, or high waters for 10 h 10 min. and 22 h 10 min., and for the low waters at 16 h 10 and 4 h 10 min.

Notice: pole star in the north and Maltese Cross on the East 

-see next diagram for the text transcription-

The initials P and B are arrayed around the respective circular crowns to
indicate the time of high tide (P) and low tide (B) in each place depending on
the position of the moon.
One example of how to read it can be applied to sayn (Enez Sun), which
is located in the outermost circle: the P is at NNE and SSW, indicating that in
full moon and new moon the high tide arrives at 1:30 am and pm; four sectors
or six hours afterwards we find B, which shows low tide. The brief introductory
text refers to the coasts falling between Beg ar Penmarc’s (Brittany) and
Gibraltar [?], and along these coasts high tide is recorded with the moon
NE/SW (at 3 o’clock sharp) and low tide when the moon is NW/SE (at 9 o’clock
sharp), a largely accurate observation (Howse, 1993). (source: Vicenç M. Rosselló i Verger)