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The following symbol set should be used in dialling equations wherever possible. In computer programs and spreadsheets, where Greek symbols cannot be used, the capitalised version should be used instead. The sign conventions and reference points for the various parameters are given in the main glossary.


Preferred symbol Alternative



(a) Co-ordinates on the celestial sphere, etc.
RA Right Ascension of a celestial body angle or time
DELTA, DEC declination of the Sun (or other celestial body) angle
ELON ecliptic longitude of a celestial body angle
ELAT ecliptic latitude of a celestial body angle
EPS obliquity of the ecliptic angle
ec EC eccentricity of the Earth’s orbit dimensionless
s S Sun’s semi-diameter angle
(b) Observer’s local co-ordinates
LON longitude (terrestrial) (positive west of Greenwich) angle
PHI, Lat latitude of a place angle
h HA hour angle (p.m. hours give positive angles) angle
A AZ azimuth of the sun (clockwise from S) angle
a ALT altitude of the sun angle
z ZD zenith distance angle
PA parallactic angle angle
(c) Sundial parameters
d DEC declination of a wall (E negative, W positive) angle
i INC inclination of the dial plate (horiz. to back of dial) angle
v V angle between noon line and angle of greatest slope for a declining, inclining dial angle
SH SH style height or angle from dial plane (note unusual use of “height”) angle
SD SD sub-style angle from noon line angle
DL DL difference in longitude angle
X HLA hour line angle from noon line (positive for pm) angle
N NH nodus height above dial plate (or length of vertical style) distance
(d) Time related
E EoT Equation of Time (as a time) time
Ea EoTA Equation of Time (as an equivalent hour angle) angle
t T time (subscript shows which system) time
LAT LAT or L.A.T. Local Apparent Time time
LMT LMT Local Mean Time (LAT corrected for EoT) time
ST ST Standard Time (LMT corrected for longitude) time
TDT TDT Terrestrial Dynamic Time time
TZ TZ Time Zone number (integer) dimensionless
tsr, tss TSR, TSS times of sunrise and sunset time
JD JD the Julian Day number days
SDT sidereal time time
ST ST standard time time
ET ET ephemeris time (obsolete) time
UT or UTC UT Universal Time (Co-ordinated) time
GMT GMT Greenwich Mean Time time
DST DST Daylight Saving Time time
BST BST British Summer Time time
(e) Co-ordinate systems
(x, y) X, Y cartesian co-ordinates of a point on the dial plane w.r.t. the origin. Optionally, (x, y, 0) in 3-D length, length
R, THETA polar co-ordinates of a point on a dial plane w.r.t. the origin length, angle
hec HEC hectemoros angle angle
hor HOR horarius angle angle
(f) Miscellaneous
MU refractive index dimensionless
Ro R0 angle of atmospheric refraction angle
T TEMP temperature Kelvin


Notes: is traditionally used for both terrestrial and ecliptic longitudes. In the rare cases where this could cause confusion, they should be denoted t and e, respectively.

Pages: A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
Introduction    Dial types    Hours (types of)    Time (types of)    Illustration
Symbols    Equations    Biographies    Chronology    Sources    Appendices