The two nomograms are presented here, GUN & GIN. The names, (GUN = Gnomonic Universal Instrument and GIN = Gnomonic Instrument Nomographic) are poor!
They were developed as a fun exercise in laser engraving/cutting using cheap MDF and acrylic. They have little or no practical use - but, nevertheless, will provide the Longitude corrected Equation of Time correct to a within a few seconds.
The author was looking to improve on the EoT device used in Pilkington's Sol Horometer where the Equation correction was incorporated by an ingenious nomographic rotation and lineation.
GUN : GNOMONIC UNIVERSAL NOMOGRAT
A large impractical device. It works for any day in the 4-year leap cycle and for any Time Zone. It provides the Equation of Time, Longitude Corrected Equation and Time of Solar Noon.
The GUN is made of three layers of 4mm high quality MDF. Each layer is separated by 0.5mm PTFE, providing lubrication to the rotating central section. The centre section is rotated by a little cog (not visible in this image) located on the brass axle seen top right corner.
GIN : GNOMONIC INSTRUMENT NOMOGRAPHIC
Another poor name, but a practical Device - set up to cover the longitude range of Gt Britain and Eire.
This slide rule was built of a base of 4mm MDF, a layer of 2mm PTFE and the top & slide of 4mm MDF. The alidade was 3mm Acrylic. It's operation is shown below.
The algorithms used provide the EoT are within +/- 1 second precision. If the device were perfectly made, the results can be read to within almost that precision, using the provided Verniers
If anyone wants the graphics to make GIN or GUN, the author would be happy to provide them with the art-work (for their specific time zone, in the case of GIN). Use the Contact button on the left.