metres temp C date time
83.259 18 24/03/11 03:30 PM
83.256 17 24/03/11 05:00 PM
83.256 8 25/03/11 08:30 AM
83.259 8 28/03/11 08:40 AM
83.256 8 28/03/11 08:55 AM
83.258 10 28/03/11 09:35 AM
83.256 11.5 28/03/11 10:30 AM
83.259 11.5 28/03/11 11:30 AM
83.256 16 28/03/11 04:00 PM
The variation includes both the variation of the instrument, stated to be the sum of +/- 1 mm plus +/- 0.005% of the length, and also the accuracy of positioning the plumb bob over the nail which may be of the order +/- 1 mm.
There is no indication of a significant thermal coefficient in these readings.
These results are rather similar to the reproducibility of a 50m steel tape used in two lengths over 100m, but without the hassle of temp corrections, end corrections and tension measurements as well as scrabbling around on the ground, all of which are needed for steel taping.
The next test will be comparison of measurement of a 250m cal course with the Bosch laser distance meter and with a steel tape.
Here is how I attached the plumb bob to the back of the laser meter:
