Universal Multi-Dial

Construct this unique instrument and you can read Solar Time simultaneously on four of the most common sundials. As an introduction to sundialling for beginners this project will develop several important concepts.

By Tony Moss, March 2014

Introduction

The initial inspiration for my Educational Multi-Dial arose from a diagram in 'Sundials' by Frank W. Cousins. My own design progressed through plywood and MDF construction in pursuit of something that could be made in schools but most were beyond the modest equipment found in the classroom.

The most significant problem, pointed out in a Sundial Mailing List exchange with teachers, was that there was no adjustment for latitude with my earlier versions. In pursuit of this I began to consider a latitude-adjustable cardboard dial assembly made from discarded breakfast cereal packets with pre-printed paper faces attached. This promising idea came to a dead end when Kelloggs U.K. were unable to fit it into their programme. Trimming the base to pre-printed degree lines solved the latitude adjustment so a dial delineated for 50° at the English south coast could be cut and sloped for any latitude up to 60°. At each stage the gnomon remains parallel to the earth's axis and the dials reads true.

When Fred Sawyer of NASS pointed out that the 50° delineation was useless in the USA it was time for a complete re-think to include three dials covering 30° to 60° north. At the same time I altered the approach so that e.g. the UK/Canada version was delineated for 60° rather than 50°. This improvement meant that the vertical dial face sloped backwards rather than forwards on adjustment and looked more natural.

Instructions

To reproduce a Multi-Dial for your latitude you will need the four printouts for your latitude covering the dial faces and the supports, a small selection of tools and suitable glues, and stiff card (e.g. from cereal packets).

Construction is simple but calls for careful work with a very sharp knife and steel rule. This is work for adult fingers using a safety rule (see my picture) if possible.! Practice on scrap material before attempting the final version. The assembly diagram and photographs should cover most other aspects.

Geographical note: although designed initially to generate educational dials for the UK, USA and Canada, these multi-dials will work equally well in Europe, Russia, China, Korea and Japan at ±0.5° of any local latitude between 30° and 60° north.

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