A new hypothesis :- )
If we move a dial holding it parallel to itself, we can bring it in a point on the Earth's surface in which it is horizontal (Equivalent Point) The longitude of the equivalent point of a vertical declining plane (longitude related to the place in which is the dial) is given by the same formula that gives the hour angle of the substyle line: tan(Long_Eq)=tan(Decl)/sin(Lat) For this reason the value found by Fer de Vries (35.7504) is also the value of the longitude of the equivalent point. Since the letter I (in PI Long.) can be the lower-case L , the writing could be read as "Plane Longitude" or the longitude of the plane parallel to the dial and tangent to the Earth's surface. Luckily we are in many to have a fervent imagination J Best Gianni Ferrari
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