Serious mistake

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In measurement technology and in the natural sciences, a gross error ( blunder ) is a measured value whose measurement deviation due to an oversight or external influence significantly exceeds the usual spread of the measured values.

Typical examples are meter errors when reading a tape measure or degree errors in angles and temperatures. Sometimes there is also a mix-up of measurement or target points or sign errors of reduction data. External disturbances can e.g. B. the yielding of the subsoil, an undiscovered axis inclination or displacement of the measuring device or a sudden unrest in the air .

While the inevitable small measurement errors (now referred to as measurement deviation in DIN ) are randomly distributed and therefore statistically compensate for averaging or computational adjustment , this is not the case with gross errors. They distort the result or the calculation model on one side (as well, but more than a systematic error ) and must therefore not be subjected to adjustment.

Gross errors and the like can be detected. a. by

  • an overdetermination - d. H. excess measurements that reveal the gross error through a contradiction. examples are
    • the measurement of barriers between recorded points
    • the measurement of arrow heights on curves or curved surfaces
    • Check with intersections of straight lines (see alignment )
    • Comparison with previous measurements
  • a preliminary adjustment of the model and then
    • Viewing the residual deviations ( residuals ). Serious mistakes are noticeable in that they i. d. Usually exceed 3 times the standard deviation
    • Targeted omission of individual "suspicious" measurements until the mean errors are in the expected range
  • Robust estimation methods , data snooping , etc.

See also

literature