Editing Sundial (section)

===Foster-Lambert dials===
The Foster-Lambert dial is another movable-gnomon sundial.<ref>{{harvp|Mayall|Mayall|1994|pp= 190–192}}</ref> In contrast to the elliptical analemmatic dial, the Lambert dial is circular with evenly spaced hour lines, making it an ''equiangular sundial'', similar to the equatorial, spherical, cylindrical and conical dials described above. The gnomon of a Foster-Lambert dial is neither vertical nor aligned with the Earth's rotational axis; rather, it is tilted northwards by an angle α = 45° - (Φ/2), where Φ is the geographical [[latitude]]. Thus, a Foster-Lambert dial located at latitude 40° would have a gnomon tilted away from vertical by 25° in a northerly direction. To read the correct time, the gnomon must also be moved northwards by a distance

:<math>
Y = R \tan \alpha   \tan \delta \,
</math>

where ''R'' is the radius of the Foster-Lambert dial and δ again indicates the Sun's declination for that time of year.