सिद्धान्तशिरोमणि: गणिताध्याय (भास्कराचार्य - ग्रहगणित, मध्यमाधिकार व स्पष्टाधिकार सटीक)

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∴ Sin EMA = a/d sin ẐAM = ÊMA expressed in radian
measure since ÊMA is very small
∴ ÊMA (expressed in radian measure) = a/d sin z I where
z is the apparent zenith-distance of the Moon ie. zenith-
distance as seen by the observer (in contradistinction to
the geocentric zenith-distance of the Moon namely ẐEM).
In particular, when z = 90°, ÊMA = a/d which is the
maximum parallax known as the horizontal parallax ie.
the parallax when the Moon is situated on the horizon of
the observer. Also the parallax is zero when M is situated
at Z as is seen from formula I and as is rightly remarked
by Bhāskara in the words 'खमध्ये नास्ति लम्बनम्'.
In fig. 91, ÊMA is the angle by which the line of
sight of the observer namely AM is depressed from the
geocentric line of sight EM. Since the plane of the paper
represents a vertical through the Sun and the Moon, the
depression of either the Sun or the Moon or the excess of
the depression of the Moon over the Sun are all in the
vertical plane. This depression is called Drik-lambana
because it is a lambana or depression in the Drik-maṇḍala
or vertical.
This Drik-lambana varies as sin z as is seen from
formula I where a, and d may be taken to be constants.
(Both a and d vary slightly a varying slightly from place
to place on the Earth, the Earth being an oblate spheroid,
and d varying from position to position of the Moon).
The maximum horizontal parallax is given by a/d in
radian measure which is equal to, according to Bhāskara's