Time extrapolating factor used in the estimation of total fishing effort. It is boat/gear specific and defined as the number of days in a reference period (e.g. a calendar month) during which fishing activities are "normal". Usually this variable is defined in reverse manner, that is by subtracting from the calendar days those days known for zero or negligible activity. Definition of active days is in itself a sample-based survey involving several sites and boat/gear types, but it is often specified at minor stratum level by means of empirical knowledge and/or information from the enumerators.