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    Re: Benchmark accuracy
    From: Bruce J. Pennino
    Date: 2018 Sep 22, 20:59 -0400

    I assume this is an original USGS BM of a particular classification.  I recollect USGS has several categories of BM based on their x,y or xyz precision and accuracy.  Now in many states, the "exact" location of a BM is tied into a state  grid. I assume the grid used by modern surveyors is correlated/corrected/tied into the GPS grid. Everything is moving relative to stars?, so knowing where something is EXACTLY is relative to the "primary" olden day BMs, which of course also move. Furthermore the "original"  Z reference of  zero based on mean tide levels along the east coast also has moved and the mean tide has moved.  And the original BMs have moved. Brain strain comes very quickly.

    I guess it all depends on the reference grid of the GPS and the BM to know exactly which is correct. Geodesy in today's world is extremely complex with various math models and corrections.......I think i need a drink ( or someone to explain it to me). Regards to all. Autumn arrives here shortly. Bruce


    From: "John D. Howard"
    To: bpennino.ce@charter.net
    Sent: Saturday September 22 2018 8:17:28PM
    Subject: [NavList] Re: Benchmark accuracy


    No, my Garvin handheld never shows better than ten feet or so - about the same as my Samsung tablet.  My son-in-law used the company unit that had radio contact with several other waypoints ( ? ) along with GPS.  His boss gets positive credits for the public service of remeasuring monuments.

    John H.

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