NavList:

1.   It is possible to pre-calculate a sextant setting using a Bygrave slide rule.

2.    It is possible to preset a box or frame sextant to the pre- calculated value.

3.    Monitoring time, it is possible, using the right hand, to bring the sextant to the eye, and note the error using the sun's disc.

4.     If the sextant is brought to the eye a few times just before the appointed time, one's body is better prepared.

5.    Knowledge of Motion of Body, and motion of the vehicle give advance warning of whether it is all working out.

6.    It is possible to do this in about 5 seconds.  

7.    Mental arithmetic may give instant values for cross track or distance run, without plotting.

8.   It is possible to fly a basic biplane whilst doing the above, hoping the engine keeps going, you don't fly into the sea, you don't fly into cloud, and you don't hit another aircraft, in the 5 seconds it takes.

9.   Compass error can be seen by pointing the lower wing trailing edge at the sun's horizon position.

10.   Accuracy is well within the limits of visibility, if the Metman was right.  It may not all work out.