June 2012 page 36
Ortwin Feustel

Ivory Sundials of Nuremberg Incorporating a Scaphe Sundial

This article analyses the scaphe sundial component found in Nuremberg ivory diptych sundials. It uses vectorial representation and measured photographic distances to determine the intended latitude for three examples, concluding that Reinmann and Miller's scaphes were likely designed for 49° latitude, and Lesel's for 48°, primarily for Nuremberg.
Dials: Scaphe, Historical Dials, Mathematics of Dialling, Sundial Design & Layout

June 2010 page 7
Ortwin Feustel

A Vertical South Sundial Indicating the Equation of Time and its Terms

This paper describes a vertical sundial designed to indicate the Equation of Time (EoT) as a figure-of-eight curve, along with its anomalistic and tropical terms. It provides the mathematical formulae for calculating these values and their graphical representations as functions of time and the sun's declination.
Dials: Vertical, Mathematics of Dialling, Construction Projects, Equation of Time

June 2009 page 14
Ortwin Feustel

The adjustment of wall mounted vertical dials

A technical article presenting a detailed mathematical method for correcting the alignment of a wall-mounted vertical sundial that has been installed with an inaccurate declination. It provides the necessary formulae and a worked example to calculate the required angle of rotation for adjustment.
Dials: Vertical, Mathematics of Dialling, Sundial Design & Layout

September 2009 page 26
Ortwin Feustel

A vertical sundial indicating the present ecliptic positions of the constellations

Describes the design and markings of a complex vertical sundial. In addition to time, the dial indicates the current ecliptic positions of the constellations using a Mercator projection. It also features longitude correction, an Equation of Time curve, declination lines, and functions as a nomogram for identifying constellations visible at night.
Dials: Vertical, Equation of Time, Mathematics of Dialling, Sundial Design & Layout

June 2008 page 92
Ortwin Feustel

A Vertical Arachnidean Sundial Indicating Islamic Prayer Times and the Direction of Mecca

This paper describes the design of a vertical south arachnidean sundial to indicate Islamic prayer times (Zuhr, Asr) and the Qibla (direction to Mecca). It explains the astronomical principles and mathematical formulae used to calculate the specific prayer curves and Qibla curve, making it readable from a significant distance.
Dials: Vertical, Historical Dials, Mathematics of Dialling, Sundial Design & Layout

December 2008 page 184
Ortwin Feustel

The Logarithmic Spiral as the Basis of a Polar South Sundial

This article proposes the logarithmic spiral as the sole mathematical function needed for designing a polar south sundial, where one spiral segment forms the gnomon profile and another acts as the dial face. It details the spiral's characteristics, equations for tangents and arc lengths, and presents a calculation example for a model, illustrating its construction and operation.
Construction Projects, Dials: Polar, Mathematics of Dialling, Sundial Design & Layout