Instructions For Special Cases.
===============================

If, after the second operation, the azimuth is
found to be between 85° and 95°, the determination of 
the altitude by the usual method would not be very
accurate, and the whole of the calculation should be 
repeated interchanging the declination and latitude
throughout. The A angle obtained will not be the azimuth
but it is used in the same way to obtain the altitude.
The same method can be used to deal with declinations
of less than 30 minutes, and for checking the altitude
obtained by the usual method.

If the hour-angle is within 20 minutes (arc) of 90°
the dead reckoning position should be changed by 30
minutes (arc) of longitude, so that the hour-angle comes
within the range of the scales.

Instructions for Normal Cases.
==============================

With the pointers in the zero position (against the
stop) turn the inner cylinder until the declination is
opposite the long pointer (L), move the ring until the short
pointer (S) is set on the hour-angle (in degrees), and read "y"
at L. The scales are numbered backwards from 90° to
180°, and if the hour-angle is greater than 90°, "y" is read
off greater than 90°. If the declination and latitude are
the same name, add "y" to the co-latitude to obtain "Y", if
the declination and latitude are opposite names subtract
"y" from the co-latitude to obtain "Y". Set S to "y", turn inner
cylinder until the hour-angle is at L, set S to "Y" and read
off the the azimuth at L. If "Y" is greater than 90°, the azimuth
is read off greater than 90. Set S to the azimuth, turn
inner cylinder until "Y" is at L, move the pointers back
to stop and read the altitude at L. These operations
are set out in concise form at the base of the
pointers.