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The prudent navigator acknowledges all sources of input.  The one you ignore 
might just be the one that kills you.

Personally, I work out my twilight sights by hand.  I estimate the midpoint of 
twilight using the Nautical Almanac, calculate the current location of the 
planets and then using 2102-D, select the navigable bodies.  This, of course, 
suffers from a distinct lack of resolution due primarily to the 10 degree 
increments in the blue overlays.  As such, the very next step is to 
re-calculate Hc for each of the selected navigable bodies via my Bygrave 
MHR-1 slide rule (only good to 1 arc minute, but it is fast).  The 
preparation, even using the MHR-1, takes me about 1 hour.  The round of 
sights ensues.  I then work out my position using HO229, which offers the 0.1 
arc minute result.  This could just as easily be calculated with the MHR-1, 
but I like switching and that was the last official set of tables produced.  
I move to the plotting board and create my fix, just like Dutton demands.  
All by hand and.whew.  The navy had quartermasters to work this out so it 
didn't take all night.

Naturally, I have all of these worked out in spreadsheets (Even the 2102-D. I 
have created what I call the 2012-E, which graphically permits me "any" 
latitude blue overlay.  What an interesting waste of time that was!  I can 
even put southern overlays on the northern hemisphere.  Bonus question, what 
does the 90S latitude overlay look like on the northern hemisphere base?  
Hint: "azimuthal equidistant charts") and check my hand work.  It is quite 
easy to make an arithmetic mistake, but I am getting better over time.  The 
electronics check is sweet and easy, but does not offer the satisfaction of 
working out the entire problem by hand.    Starpath will give you that quick 
result and provide that "second input".  

Finally, I compare my result to the GPS, the third input.  Always a humbling moment.  

Consistently, Bowditch in the 1800's recommends that the longitude be derived 
by all methods available.  Longitude by DR, Longitude by Lunar, Longitude by 
Chronometer, etc.  I am sure, if he were alive today, he would add Longitude 
by GPS!

I guess it all comes down to how much effort you want to put into this.  The 
navigation officer was busy all day working his position out, by hand.  The 
more electronics used, the less work and, theoretically, less prone to human 
error.  The Navy recognized this and has moved forward.  Tally-ho!

As each bit of electronics is added, however, the more it becomes a black box. 
 Taken to the limit, we have GPS which is nothing more than Celnav made easy. 
 Sure its high tech, position on demand, offers more resolution and accuracy. 
 But...where's the fun in that?

Best Regards
Brad



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