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    Re: A slope example
    From: Antoine Couëtte
    Date: 2010 Nov 30, 13:16 -0800

    Dear Piterr,

    Sorry for not being ore comprehensive :

    - Vega's Azimut is listed in my reference post (actually it is indicated slightly after the part you are quoting) and from my logbookbook it reads 289.3 degrees, which should be the value I quoted.

    - The HP41 Series - and certainly TI ones - as well as (almost) all other HP series have automatic ad IMMEDIATE statistics computation through punching the single function "Sigma+" key, which immediately gives you for a (x,y) pair the "cumulated values of all previous x" , i.e "Sigma x" and the "cumulated value of all previous y", i.e. "Sigma y", as well as a few other items such as (at least) "Sigma xy", "Sigma x**2" and "Sigma y**2", + Number of single data entries (i.e. the "n" number) to the best of my recollection. From these data it is fairly easy to derive both : slope of the best fit linear regression - which you can then very easily compare to the "predicted slope", as well as correlation coefficient which - if close to 1 or -1 - will indicate NO outlier, and if below @ 0.75 in absolute value will indicate one or more outlier(s). In other words, no need to tediously add up "all those figures and divide by the number of observations", it is all automatic : just hit the "Mean" key.

    So, the values I am using to-day are simply "mean value of Time" and "Mean value of geocentric heights". The Azimut and the intercept are computed for this exact quoted "Mean Value of time". It is mere coincidence if one of the single UT values "samples" almost coincides with their overall mean UT value here.

    I am not pretending that a manual slope is of no interest. I am just lazy, and have found an efficient (I think) means to replace manual slope drawings, while simply postponing manual drawings to the sole LOP's recknoned from the running fix (see a bit further down) :

    - Initially I computed correlation coefficients and I performed actual/predicted slopes comparisons. Since from experience I do not see any clear adavantage to these operations,
    - nowadays, and ONCE "flashing outliers" have been removed one way or the other, I simply "average" both times and heights. I keep the possibility of manually discarting (AVERAGED) LOP's once thay have been (manually or automatically) drawn around the "no time-tag" (i.e. runnig fix) DR position.

    PS : 14 kts for an Aircraft Carrier is just "slow average", as she can easily and routinely reach @ 30 knots.

    Hope it gives you additionnal insight. If more requested or required, do not hesitate.

    Best Regards


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