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    Re: Which Method do you prefer using and why.
    From: Greg Rudzinski
    Date: 2013 Apr 4, 08:31 -0700

    Frank,

    On point 4. where you say

    "I, personally, cannot recommend a regular slide rule to anyone contemplating celestial navigation calculations. The calculational accuracy is not up to the task, and it's only an illusion that they represent historical celestial navigation. If you like slide rules, that's a separate passion and "good fun". They have very limited value for cel nav calculations."

    I think you have sold the standard slide rule short here. You are correct that when calculating altitude (Hc) the slide rule results are not up to the task. Where the slide rule does CN better than you might think is in calculating azimuth and ex-meridian values. Until Hanno Ix gave us his diagram I used the slide rule to calculate azimuth over even using the Rust diagram in the back of Weem's Line of Position.

    Greg Rudzinski


    Re: Which Method do you prefer using and why.
    From: Frank Reed
    Date: 2013 Apr 4, 07:11 -0700
    Sean, you wrote:
    "1. HO 229 - super fast and makes me feel connected to "old" methods, which is why I like C.N. in the first place."

    Interesting irony. Those tables were first published in 1970 (give or take a year or two). They were considered the epitome of modern celestial navigation for a few brief years, and at the time it was hoped that they would sweep away the "old" methods.

    And:
    "2. Flat Bygrave - not as fast, but fascinating to me nonetheless."

    Yes. Very cool. And cheers once again to Gary LaPook for developing and promoting this very efficient system based on the old Bygrave cylindrical slide rule.

    And you wrote:
    "3. Scientific calculator - relatively quick, compact, and I already have several laying around."

    Yep. And consider these things in "historical perspective". They've been around forty years already. I got my first "scientific" calculator in 1976 for 25 bucks (almost exactly $100 in today's money after inflation). It was a TI-30 with classic (read "awful") 1970s stylings, and it was a revolutionary calculating machine. I still have it. It still works. That calculator was a common consumer item available to "kids like me" (I was in eighth grade). From the standpoint of the history of navigation, it's interesting to note that the TI-30 and H.O. 229 were contemporaries, released only five years apart. H.O. 229 was already headed into obsolescence just a couple of years after it appeared.

    And you wrote:
    "4. 'Regular' slide rule - not very accurate, but has the same appeal as the Bygrave."

    I, personally, cannot recommend a regular slide rule to anyone contemplating celestial navigation calculations. The calculational accuracy is not up to the task, and it's only an illusion that they represent historical celestial navigation. If you like slide rules, that's a separate passion and "good fun". They have very limited value for cel nav calculations.

    You added:
    "5. HO 249 - would probably be higher on my list if I just used it more."

    Pub.249 volume 1, "Selected Stars" is almost TOO easy. The calculation is so short that many people find it un-challenging and therefore uninteresting. But it's very fast and practical.

    And:
    "6. Computer/Phone app - seems to me you might as well just use a GPS. However, they are quite handy when you don't have anything else."

    Also, software and "apps" are good sight-training tools. Many students of navigation would like some instant feedback. Take a sight, tap a few keys (or a touch screen) and five seconds later you know how you're doing. That's valuable. Additionally, one "mode" of GPS failure that we should worry about more is failure, not of the local electronics, but of the satellite transmissions, due to jamming or some other active "hacking" or extreme solar interference. Many new GPS receivers (including nearly all smartphones manufactured within the past year and a half) are both GPS and GLONASS receivers so in that sense they already have a "system" backup. But I suspect (I'm not sure) that an attempt to disrupt GPS signals could as easily knock out the GLONASS signals, too. Bottom line: it's not necessarily "cheating" to have software to clear sights since you may have a situation with no reliable GPS signals but electronics functioning perfectly.

    Again I'm reminded of a point Luis Soltero made. When the GPS goes out or becomes unreliable, you immediately are faced with an odd problem: you don't know where you are. That might sound blatantly obvious, but the point here is that a GPS nav system often (normally?) has no hard-copy output of any sort. So you go from having a well-defined, exceptionally accurate track on a screen in front of you to having nothing at all. It's quite possible that you don't remember your lat/lon even to the nearest degree when the system drops out on you. It's the little things that get you! Naturally, because of this potential problem, every navigator keeps a pen and paper handy and records the lat/lon every thirty minutes and also maintains a plot on a paper chart. Naturally. :) This sort of statement is in the same category as "I back up my important computer files once a week". Boring housekeeping tasks are the perfect job for automation.

    -FER

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