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    Re: Learn the stars, by phone
    From: George Huxtable
    Date: 2009 May 22, 20:13 +0100

    Frank Reed wrote
    
    "I wrote previously that the SkyScout has a pointing accuracy of 0.5-1.0
    degrees. George found a FAQ saying 2-3 degrees. If we were talking about a
    sextant or other measuring instrument, those statements would be
    contradictory, but we're not.
    
    Under good operating conditions, I wouldn't be surprised if the SkyScout has
    a pointing accuracy at the high end of accuracy. And under marginal
    operating conditions (for example, just before its software complains about
    magnetic interference), I wouldn't be suprised if the pointing accuracy is
    near the low end of accuracy. For a device with no magnification, none of
    this makes any difference, of course. "
    
    Frank is trying hard to find a bit of "wriggle-room" here. But that wasn't
    the contradiction.
    
    In [8254] he wrote "These compasses, aided, of course, by software models of
    the Earth's magnetic field, can determine true direction in three dimensions
    in most parts of the world to an accuracy of one degree or better."
    
    and when that was questioned as seeming implausibe, he reduced the claimed
    error even further, stating- "The Skyscout ... includes a GPS chipset, two
    magnetic chipsets, and accelerometer chipsets. With the output from those,
    it can determine where you're pointing in the sky from anywhere on Earth at
    any date and time (probably limited to a few decades out for planet
    positions) with an accuracy of about 0.5 degrees."
    
    That seemed even less likely, and as I could find no such claim currently
    being made by the makers , I asked where it had been made, and got this
    seemingly authoritative reply "It refers to the SkyScout, which I have tried
    out myself. That half-degree claim comes from the official specs. It's a
    believable claim, based on performance, but the exact level of accuracy
    (whether it's 0.5 or 0.75 or 1.0 degrees) is not critical in any way to the
    device's use."
    
    So, again, I asked-
    " That is why I've been trying to find
    out-
    1. Who makes such a claim?
    2. Under what environmental circumstances is it claimed to apply? Such as
    magnetic latitude, acceleration, sensitivity to local magnetic deviation,
    temperature range?
    3. What are the snags, if any?"
    
    but got no further response.
    
    Since, then, I've found a statement, hidden away on a shadowy corner of the
    Celestron website, which belies Frank's claim for half-degree accuracy,
    stating
    
    "" Pointing accuracy and using my SkyScout
                The SkyScout has a pointing accuracy of 2-3 degrees (a thumbtip
    at arms length). It is not as accurate a pointing device as an optical
    finderscope with crosshairs, a pair of binoculars with a reticle ..."
    
    There's the contradiction. Frank informed us his quoted half-degree "came
    from the official specs". Well, did it? Did Celestron make such a claim at
    some time, then diluted it? That would be interesting, in itself. Or did
    Frank imagine it? He should either withdraw, or back it up, not try to sweep
    such a significant discrepancy under the carpet.
    
    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.
    
    
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