It is my bet the military uses the proper
math model of the earth and they do not want
the average joe to match them in accuracy
and precision when in reality the average joe
can not afford the proper equipment to make use of such
accuracy and precision.
How much does a real atomic clock cost all by itself ??

:-)
geoff

----- Original Message ----- 
From: "Stephen & Kathy" 
To: 
Sent: Friday, January 01, 2010 11:10 AM
Subject: Re: And Now A Simple Question


> Another FYI, in case you didn't notice in the notes on the USGS pages,  the IASP91 is based on what they term a 
> spherically-symmetric model, the ellipsoid is not taken into account.  Those pages are apparently not going for ultra-high 
> accuracy, just for a simple average.  I guess, they assume, those pages are close enough for government work, for the public, HA!
> Stephen
> PSN Station #55
>
> GPayton wrote:
>  Thank you, Stephen & Kathy,
>
>  No, that had not been mentioned and is good information.  I guess I could say that if it is good enough for the USGS, it should 
> be good enough for me!
>
>  However, as accurate as it presently may be, it IS a table of averages and the wave plane would still propagate differently each 
> event through different conditions within the mantle.  Therefore, as I said, either JB or IASP91 is accurate enough for my 
> primitive needs.
>
>  Thank you again & Happy New Year.
>  Jerry
>    ----- Original Message ----- 
>    From: Stephen & Kathy
>    To: psn-l@..............
>    Sent: Friday, January 01, 2010 12:56 AM
>    Subject: Re: And Now A Simple Question
>
>
>    FYI, (sorry if this was already mentioned), the USGS Earthquake time travel calculator uses the IASP91 model, as per the note 
> at the bottom of the page; see the following link.
>    http://neic.usgs.gov/neis/travel_times/artim.html
>
>    The USGS "Theoretical P-Wave Travel Times" map with shadow zones, also says it uses the IASP91 model.  Following is a link to 
> an example for the 6.0 Banda Sea quake on Dec 26...  see notes below map.
>    http://neic.usgs.gov/neis/bulletin/neic_qrat_t.html
>
>      Stephen
>      PSN Station #55
>
>    GPayton wrote:
>      Thanks to you, Larry and all that answered.  I've searched and can only find that the IASP91 is the newer, but cannot 
> discover that it would matter that much in my limited sensor setup and environment.  Looking at other posts, the JB seem to be the 
> favorite, if not be default.
>
>      Regards & Happy new Year to All
>      Jerry
>
> 

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