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    Re: Learn the stars, by phone
    From: Ken Gebhart
    Date: 2009 May 14, 16:27 -0500

    Just a note here.  As a Celestron dealer I know that the some  
    Skyscouts exhibited a fault of complaining about magnetic  
    interference even when there was none around.  Celestron replaced  
    those units when asked.  The problem was fairly widespread.
    Ken Gebhart
    On May 14, 2009, at 12:19 PM, Brad Morris wrote:
    > Hold on there!  I never claimed any pointing accuracy.
    > It works to my satisfaction.  It beats the snot out of the 2102-D  
    > method of finding the navigational stars.  Lots easier and  
    > basically more fun.  I pretty much won't use it to 1 degree in any  
    > case, the navigational stars just aren't that close.
    > The Celestron Skyscout has two basic functions.
    > 1) If you ask it to find an object, it directs you to point the  
    > device in various directions until it tells you that you are  
    > pointed right at it.
    > 2) If you point at an object, it can tell you what object that is.
    > How it determines the magnetic deviation is not divulged.  I have  
    > had the device tell me that there was a deviation when standing  
    > next to my vehicle and when I was too close to power lines.  One  
    > internet reviewer who was using it for astronomy indicated that it  
    > detected an anomaly due to a ferrous screw in his kit.  That's  
    > right, a screw. I suspect bringing a bar magnet to the device would  
    > set off the immediate complaint.  I will give this a twirl  
    > tonight.  It doesn't care what mode you are in, it just starts  
    > complaining the moment it senses the deviation.
    > To Frank's question as to how the batteries don't affect the  
    > magnetic field: there is a mu metal shield provided with the device  
    > that is placed around the batteries.  Mu metal is a well known  
    > material which actually reduces magnetic fields across its boundary.
    > Best Regards
    > Brad
    > -----Original Message-----
    > From: NavList@fer3.com [mailto:NavList@fer3.com] On  
    > Behalf Of George Huxtable
    > Sent: Thursday, May 14, 2009 1:03 PM
    > To: NavList@fer3.com
    > Subject: [NavList 8267] Re: Learn the stars, by phone
    > Thanks to Brad and Frank for their responses to my questions about  
    > magnetic
    > direction sensing, and for links to additional information.
    > I was questioning one aspect, and only that one, of the claims that  
    > were
    > being made about such a device, the ability, in Frank's words, to  
    > "determine
    > true direction in three dimensions in most parts of the world to an  
    > accuracy
    > of one degree or better."
    > If that were possible, I could see an obvious application arising  
    > on my own
    > boat, and no doubt so would many others. The marine world would  
    > beat a path
    > to its door. But I was somewhat sceptical (as usual) and asked a  
    > number of
    > questions, recommending that such claims should be taken with a  
    > pinch of
    > salt, and asked who was making them.
    >  Brad hasn't addressed that claim of 1� of accuracy, for direction,  
    > but
    > Frank has taken it further, by writing- "it can determine where you're
    > pointing in the sky from anywhere on Earth at any date and time ...  
    > with an
    > accuracy of about 0.5 degrees." , but he still doesn't state where  
    > this
    > figure comes from, what instrument it refers to, and under what  
    > conditions
    > it applies. Nor have I found any claim for such directional  
    > precision in the
    > websites I was directed to, though I may have missed it, somewhere. It
    > doesn't seem to be included in the many pages of promotional guff  
    > about the
    > Celestron Skyscout, which as far as I can work out doesn't even  
    > display the
    > compass direction it's pointed at, just names a likely star that's  
    > in that
    > direction. Have I got that right?
    > The review article that was pointed to is of little help, as its  
    > author
    > clearly failed to understand even what the accelerometers were for  
    > (they are
    > to establish which way is up).
    > Brad tells us of his satisfaction with its behaviour when used for
    > identifying stars (which is, of course, its purpose) but little  
    > about its
    > pointing accuracy. He tells us "It is sensitive to local ferrous  
    > materials
    > and in fact informs you when the deviation is greater than some  
    > internal
    > value.". I'm sceptical about that magic ability. How could that be  
    > done? It
    > could, perhaps, by detecting any significant difference in the  
    > total field
    > strength, or the dip angle, from the value predicted for that  
    > location on
    > the Earth. But could it establish, by such means, a deviation that  
    > changes
    > the magnetic direction by 1�? I don't believe it!
    > Frank, as is his style, belittles that problem by addressing it in
    > exaggerated terms- "Clearly, as you suggested, if there's significant
    > magnetic or acceleration interference (you wouldn't want to use it  
    > inside an
    > iron carousel), then it would have problems.. ". Well, of course, I  
    > wasn't
    > considering an "iron carousel", I was talking about real-life  
    > difficulties
    > that interfere with real-life compasses, difficulties that need  
    > serious
    > consideration.
    > Brad could make an interesting little project of it (except that I  
    > know he's
    > involved in several interesting projects already).  He could point his
    > Skyscout to where two stars appear, reasonably close together side  
    > by side,
    > near the horizon, and establish the threshold point between   
    > identifying one
    > and the other, by swinging the instrument a bit from side to side  
    > to see at
    > what direction it switches. Then try to fool it a bit by bringing a  
    > little
    > bar magnet towards it, from East or West,  pointing horizontally,  
    > one pole
    > towards the Skyscout,  at the same level as the instrument. It  
    > would be
    > interesting to see how far the dividing-line can then be shifted,  
    > before it
    > warns that magnetic material is present. Frank states that "It's not
    > bothered by minor magnetic interference", but to what extent has he  
    > tested
    > that, and how? What results did he find?
    > George.
    > contact George Huxtable, at  george@hux.me.uk
    > or at +44 1865 820222 (from UK, 01865 820222)
    > or at 1 Sandy Lane, Southmoor, Abingdon, Oxon OX13 5HX, UK.
    > "Confidentiality and Privilege Notice
    > The information transmitted by this electronic mail (and any  
    > attachments) is being sent by or on behalf of Tactronics; it is  
    > intended for the exclusive use of the addressee named above and may  
    > constitute information that is privileged or confidential or  
    > otherwise legally exempt from disclosure. If you are not the  
    > addressee or an employee or agent responsible for delivering this  
    > message to same, you are not authorized to retain, read, copy or  
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    > >
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