Sundials: a Simplified Approach by Means of the Equatorial Dial

accuracy altitude analemmatic dial apparent noon apparent solar armillary dial art of dialling B₁ bead Bedos Berossus BRITISH MUSEUM cast celestial equator celestial pole celestial sphere centre clock compasses correct COURTESY curve decl declination line Declination of Sun dial plate disc displacement distance draw Earth East ellipse equatorial dial equinoctial line error example fast give gnomon Gnomonica graphical construction Greenwich horizontal dial hour angle hour lines hour scale illus inches instrument latitude latitude 50 length log tan h London longitude mathematical mean meridian minor axis minutes minutes of arc NATIONAL MARITIME MUSEUM noon line noon mark parallel perpendicular plane plts Polar dial rabatted radius readily right angles rotation shadow shown in FIG sidereal day simple slow solar day substyle sun-line Sun's declination sundial theoretical style values vertical declining dial Vertical dial facing wall