Errors in Measuring Height Differences in Engineering

For classic geodetic instruments, sources of errors influencing the total measurement error were determined. In digital levels, the technique of comparing the current image of the graduated rod with the saved picture of the graduated rod is used to read the rod. This reading technique eliminates the subjective influence (operator's error), but an error occurs from comparing two images. Apart from this source of errors, several errors in rod reading are not present at classical levels. Experimental measurements with digital levels have proven that certain sources of errors, which other authors also processed, can be significant concerning the accuracy of measurements. For example, illumination at 45° or steeper angles can cause reading errors more than ten times the measurement error at the station. Or, that inhomogeneous illumination of some parts of the rod causes large measurement errors, up to a few millimetres. One source of error has not been considered so far - this is the error that arises from incorrect sighting on the rod. Experimental measurements confirmed that misalignment caused an error of the order of tenths of a millimeter, and which can be larger than the measurement error at the station. It was also confirmed that this error is not characteristic only for one type of digital level, but it is already being reported in all. This error can be greater than the mean error of measuring the height difference at the station, which is significant in engineering works where height/height difference is often measured or marked using only one station.