Three answers on one wall
sourcesimplified geometry
The sundial on the garden front of Wilanów Palace, around 1684, on the south-eastern corner pavilion. Not one dial but three: equal hours in the centre, Italian hours on the left counted from the last sunset, Babylonian hours on the right counted from sunrise.
- Equal hours
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- Italian hours
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- Babylonian hours
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- Mechanical clock
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- True solar time
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- Discrepancy
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At Wilanów the sundial and the mechanical clock never show the same hour. The gap is made of the equation of time plus a fixed correction of six degrees east of the zone meridian.
The model assumes a wall facing due south and a gnomon perpendicular to it.
Text description of the instrument
The Wilanów dial gives three readings from a single shadow: equal hours, Italian hours counted from the last sunset, and Babylonian hours counted from sunrise. True solar time at Wilanów never agrees with a mechanical clock — the gap runs between roughly ten and forty minutes across the year.