NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: sight reduction calculator
From: Jeremy C
Date: 2008 Jun 21, 04:53 EDT
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From: Jeremy C
Date: 2008 Jun 21, 04:53 EDT
In a message dated 6/20/2008 7:48:36 A.M. West Pacific Standard Time,
glapook@pacbell.net writes:
Gary LaPook writes:
I have no idea how it could take ten minues to calculate Hc and Zn on a pocket digital calculator, I just did a sample test and it took me 58 seconds. I use the standard formula for Hc rearranged to the form:
Hc = arcsin (cos LHA x cos dec x cos lat + sin lat x sin dec)
and Z = arcsin (sec Hc x sin LHA x cos dec) since implementing it this way saves a few keystrokes. Using a TI-30 with only 3 memory locations the key strokes are:
(When entering values in the format of degrees.minutes seconds, change decimal minutes to seconds, 6 seconds per tenth of a minute, in your head before punching in the assumed latitude, declination and for the GHA and assumed longitude entries.)
Assumed Lat
2nd DMS-D.D (changes to decimal degree format)
STO 1 (stored A. LAT in 1)
Declination
2nd DMS-D.D
STO 2 (stored DEC in 2)
GHA
2nd DMS-D.D
-
Assumed Longitude
2nd DMS - D.D
= (computed LHA)
STO 3 (LHA stored in 3)
COS
X
RECALL 2 (recalled declination)
COS
X
RECALL 1 (recalled Assumed latitude)
COS
+
RECALL 1 (recalled A. LAT)
SIN
X
RECALL 2 (recalled DEC)
SIN
=
2nd SIN (ARCSIN, computed Hc)
STO 1 (stored Hc in 1) (you won't need the stored A. LAT again)
COS
1/x (converts COS Hc to SEC Hc)
RECALL 3 (recalled LHA)
SIN
X
RECALL 2 (recalled DEC)
COS
=
2nd SIN (ARCSIN, computed Z)
RECALL 1 (recalled Hc)
2nd D.D - DMS (changed Hc in decimal degrees to degrees, minues and seconds)
da-da!
done
58 seconds flat..
gl
Jeremy writes:
Included in my time is the whole reduction including looking up the GHA,
and Dec in the NA then dealing with the various differences and finding
LHA. The actual entry into the calculator and computation is indeed a
matter of seconds, even on my incredibly slow NC-2. In my TI-85 with its
straight entry of trig functions, it probably takes me about 30-40
seconds. The longest thing is converting the minutes and tenths into
decimal degrees and saving them as variables.
Jeremy
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