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Fig 3.

To calculate the date of construction

  1. Assume that the scale is linear arround the time of the equinox (near the end of March)
  2. Using the step between the 1st of April and the 1st of September. The number of days is given by :- (58.5 - 53.5) x 31 / (58.5 - 42.25) = 9.53 days
  3. From the ladder calendar for the year 325 AD. the corresponding number of days from the 1st of April to the 1st of September is 12.
  4. Therefore the calendar has slipped by :- ( 12 + 9.53 ) / 2 = 10.76 days
  5. The Julian calendar was adding an extra day every 128 years. So a slipage of 10.76 days is equal to a time of 128 x 10.76 =1377 years.
  6. Then the date of construction = 1377 + 325 = 1702 AD.

Fig 3. North face of the small cross at Sandbach