1882 US PBM
The rods are 3 meters long, made of two pine boards with a T-shaped cross section, with an iron spur at bottom with a flat end, and a watch level by which to
hold it vertical. They are graduated to centimeters, and are read by estimation to millimeters. No target is used.
Average daily run in miles for working days........ 2.9
SAINT Louis, September 1, 1883.
SIR : I have the honor to submit the following report of the field work of precise levels from Grafton to Chicago. This work was done in three seasons, viz:
I. Grafton to Keokuk, 151 miles, done May 21 to August 30, 1881.
II. Keokuk to Fulton, 170 miles, done September 6 to November 25, 1882.
III. Fulton to Chicago, 170 miles, done May 2 to August 7, 1883.
At Clarksville and Port Louisa the crossings were effected by simultaneous readings with two instruments on opposite sides of the river, the midwire bisecting a large target on the opposite shore. Sixteen readings were taken by each instrument, in sets of four, which were as follows:
1. Telescope normal, level direct.
2. Telescope normal, level reversed.
3. Telescope inverted, level direct.
4. Telescope inverted, level reversed.
Then each observer, with his instrument, crossed over, and the same was repeated. The longest readings thus taken were about 600 meters. Very good results were
obtained, the probable error being less than a millimeter.
Maybe the new NGS river crossing method isn't so new.
Many of the original surveyors were immigrants from the other side of the pond where meters were the standard.
Many a property was measured in meters with a meter tape or chain because it was what the surveyor had and everything was reported in the required unit of measure of the region they were working.
There were also the varying length of tapes and chains that were mixed up and used resulting in the report of the wrong distance of many original surveys.
In the late 1960s the surveyor that I first worked with only had vara tapes and we would compute the feet values when the State of Texas began its move from varas to feet in their reports.
Every construction site I've worked on all the plans were in feet and inch and we always used feet and tenth tape for the layout.
Here is the start of transcontinental leveling in the US: https://www.ngs.noaa.gov/cgi-bin/get_image.prl?PROCESSING=get_figure&IID=274994
And this history of geodetic leveling in the US: https://geodesy.noaa.gov/PUBS_LIB/History_of_Geodetic_Leveling_in_the_US.pdf
Reading the most recent recovery note on the point’s datasheet, I see mention that the site might not be suitable for GPS. Sheesh. I never trust these suitability reports. Clearly NOT usable for GPS.