difference between the instantaneous knowledge error at a given time, and its mean value over a time interval containing that time
NOTE 1 This is expressed by:
NOTE 2 As stated here the exact relationship between t and Dt is not well defined. Depending on the system it can be appropriate to specify it more precisely: e.g. t is randomly chosen within Dt, or t is at the end of Dt. See annex A.1.4 for discussion of how to specify the interval Dt, and annex A.1.3 for defining requirements on the knowledge error.