Vertical dial

As its name indicates it, the vertical sundial has its vertical table. The style must be parallel to the axis of the Earth and the dial must be directed so that the style is in the plan of the local meridian line. The line of midday, always vertical, thus materializes this local meridian line. When the plan of the dial makes exactly vis-a-vis the south, the dial is known as southernmost or not declining. When the plan of the dial is directed in an unspecified way, the dial is known as ''' declining '''.

The angle $\ gamma_H$ between the time lines and the line of midday depends on the Latitude as well as time angle H, i.e. the angle which the sun with the local Méridien forms.

For a dial not declining the angle $\ gamma_H$ is given by the formula $\ tan \ gamma_H= \ tan H \ cos \ phi \$

Contrary to the case of the equatorial Dial, the angle $\ Delta$ between two successive time lines, corresponding to two time angles H1 and H2, is not constant. The difference $\ Delta$ = $\ gamma_ {H2}$ - $\ gamma_ {H1}$ can be expressed according to H2 and H1 starting from the preceding formula.

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