July 1991 page 38
Hector Parr

Sundial Calculations for Computer Programming

This article presents the theoretical basis for a computer program designed to calculate hour lines for various northern hemisphere sundials (direct, declining, vertical, reclining, inclining). It outlines using spherical trigonometry formulas to determine dial plane elements and hour line angles. The author emphasizes robust programming to handle issues like division by zero and inverse trigonometric ambiguities, providing simplified BBC Basic and design guidance.
Dialling Tools, Mathematics of Dialling, Sundial Design & Layout

October 1991 page 36
Hector Parr

Computer Program Listing

This section provides a listing of a BASIC computer program by H.C. Parr for calculating sundial hour lines, intended to accompany a previous article. The program is designed to save time and prevent errors in sundial computations. Details for obtaining the program on a 5 1/4 inch disk and information about inputting latitude, reclining angle, and declination are included.
Dialling Tools, Mathematics of Dialling