An Ancient Rule for Making Portable Altitude Sundials from an ‘Unedited’ Medieval Text of the Tenth Century

The existence of other altitude sundials of the same kind seems to be confirmed by the words used by Byrhtferth of Ramsey (c. 970 - c. 1020) in a passage of his Manual: "the sun ascends point by point on the sundial", and again "Observe, O clerk, how the sun ascends point by point on the sundial".2 To the same monk was attributed, in 1563, the Glossae to the De temporum ratione of the Venerable Bede (627-735);3 in these we read: 'The point [one of the fractions of one hour] is so called from the word 'pungendo'; because of this they make some points on the sundials.