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    Re: Vertical Angle Measurement Errors
    From: Bruce J. Pennino
    Date: 2013 Mar 30, 09:30 -0400
    After looking at the data, total bounds of scatter, means, standard deviation (sigma(n-1)), etc, I have the following preliminary conclusions .  Opinions,     please.
    1.  Moving the index up or down for a reading does not influence results as far as I can see. Any discrete small  slack (procedural error) is overwhelmed by other errors. So I won't worry about which way I'm moving the index.
    2. With the possible exception of the data recorded on the strap (tank), the data does not lend itself easily for precise determination of collimation error.  The "strap" vertical angle measurements data seem to indicate collimation error is very small, maybe a second or two at most,   so all angles will be measured in normal /front viewing mode.
    3.  The standard deviations indicate that at least 5 or more (maybe 10) sights must be averaged.If the surface is irregular or lumpy an averaging technique must be followed.   Probably will try to measure to top of surface over time.
    4. To prevent overlap of error bands, when changing my height of eye I should move vertically at least the equivalent of 30 seconds of arc,  and 45-60 seconds is even better; if possible. For example, if  set of data has a height of eye of 10 ft , the next set of data should be taken with an h of 14 ft at least.  If there are waves, an even larger vertical movement should occur. Try to do on calm days or in bays. 
    Wave height, temp, wind, time, tide etc will be observed/recorded.   Knowing how variable waves can be,  an effort will be made via the angle measurements to estimate wave height where sighting.

    ----- Original Message -----
    Sent: Thursday, March 28, 2013 11:15 AM
    Subject: [NavList] Vertical Angle Measurement Errors


    I've attached some angle data I've recorded with my theodolite. My goals are stated. I'm in the process of evaluating this information, and hope that others will look it over. I'll post my conclusions in a couple of days, and then we can discuss further. I've tried to give all pertinent information within the attachment.

    A very little about the data..... No data points were excluded and there are no apparent blunders. There are some outliers. The data was recorded very carefully by reading the angle, rereading, writing it down, recheck reading, recheck writing, and then going on to next point. It only takes maybe 1 minute per value, so it goes quickly once the instrument was set up. The device is an earlier total station which requires "eyeball" reading of an index....no digital output. The instrument calibration is extremely stable, but it has not been to a shop in 10 years. I check it frequently in various ways, especially against other work I do with another instrument; or on occasion against work done by a professional land surveyor I know who is an absolute fanatic about precision, accuracy,errors,etc.

    We are starting to learn a little. I hope to go next week and measure dip from a precisely known elevated position, Blue Hills Observatory outside Boston.


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    Attached File:
    f1-Topcon-Error-Determination-D.doc (no preview available)

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