Difference between the measured value and a limit value. Each measured value — and therefore each measurement result — is influenced by any imperfections associated with measuring instruments and measuring devices, the measuring procedure and the measured object; there are also influences from the environment and the observer whereby time differences associated with these influences play a part too (Figure M 16).
A distinction is made between random and systematic deviations and again between known deviations — which can be factored in — and unknown deviations, which can, however, be estimated (Figure M 17).
Known systematic deviations include accuracy data for a measuring instrument. They are expressed as a % of the limit value for the measuring range or in terms of the current value at that point in time. These will differ from each other quite significantly, particularly in a range containing small measured values, so considerable care is required.
Figure M 16: Measuring error for a position measuring system
Figure M 17: Relationship between measuring error and measurement uncertainty