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Author
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Topic: LHA calculation
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DustyDan
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posted July 20, 2007 10:17 AM
I missed the rule on calc. of LHA. If negative, add 360, and in example getting 330. Then as I go to the table it lists numbers progress through about 99-115 degrees, then truncates. Problem answer in the book uses Hc that would correlate to using 30 degrees. Is there a rule that tells me what LHA to look up when the calc value is 330? ThankQ
From: North Dakota
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David Burch
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posted July 20, 2007 11:00 AM
I am not sure i follow the question exactly, but it makes me think of one we often do get. Namely, that when you enter any set of sight reduction tables you need to look on both sides of the page for the LHA you care about. Entries like 330 and 30 will be on the same line, labeled one way on one side and the other way on the other side.
If that is not the point at hand, please give us a specific example to work on. thanks.
From: Starpath, Seattle, WA
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DustyDan
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posted July 27, 2007 10:55 AM
I got it, sorry, stupid question. Thanks.
From: North Dakota
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David Burch
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posted July 27, 2007 11:53 AM
Do not hesitate to ask your questions. It is the great value of the online format that we are able to help.
From: Starpath, Seattle, WA
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OLowry
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posted August 29, 2007 04:58 AM
I'm also having problems with the "if nagative, add 360" rule. I have tryed to find a clear statment about this rule but can't find one (that I understand), Can you help? For some reason my mind is hung up on if I have a 330 and add 360 that gives me 690 so what am I to do with that. Please help I'm hung uo on the diffrent ways to Cal. LHA. Thanks
From: Indianapolis, IN
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David Burch
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posted August 29, 2007 09:42 AM
We might be best here with addressing specific examples that are troubling you, so if you give those we can use those as the exact examples.
also, i am guessing this is a matter of the angle arithmetic rather than the LHA concept, so it might be valuable to review the rules from chapter 1 (i think these are what you are looking for), namely AA-3 and AS-3 given on page 1-12.
here are a couple quick examples, not related to LHA alone, but also later in the course for figuring GHA of stars, and other places...
250 + 30 = 280 which is less than 360 so OK
250 + 100 = 350 which is less than 360 so still OK
250 + 150 = 400 which is more than 360, so the right answer is 400 - 360 = 40
now subtraction:
250 - 50 = 200 which is greater than 0 and less than 360 so OK
250 - 200 = 50 which is again OK, ie a positive number less than 360
250 - 300 = -50 this is a negative number, ie it is less than 0, so to get the right answer we must correct it by adding 360 and the right answer is -50+360 = 310.
From: Starpath, Seattle, WA
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bruce
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posted March 07, 2020 08:32 PM
"when you enter any set of sight reduction tables you need to look on both sides of the page for the LHA you care about. Entries like 330 and 30 will be on the same line"
I *love* this forum. I worked through the exercises in chapter 5 today, and 5.3 #4 threw me for a loop because I couldn't find a row in the table for LHA=330.
Quick search here and the mystery was solved. I *never* would have thought to look for another column of LHAs on the right side of the page.
Thank you!
Bruce
From: Everett, WA
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