PIERCED STYLE DIALS
In this class, the each half of the analemma is encoded in either side of the style.
THE INTEGRATED DOUBLE GNOMON SUNDIAL OF WERNER RIEGLER
This unique idea has been realised in 2003 by Werner Riegler in Joannes Kepler's city of Linz.
For more detail, read below
ERRORS USING A SINGLE SYMMETRICAL GNOMON THROUGHOUT THE YEAR
Werner Riegler has analysed this situation in the following paper. In summary, a symmetrical gnomon can be made that will work with errors not exceeding 1.7 minutes of time. However such a gnomon will not work for some 10 days around the winter solstice and for some 2 days around the summer solstice. During these periods, the correction for one day shadows the correction of the next day. Thus, such a gnomon can only exist the declination range -23.30° to 23.42°