A 'not elsewhere classified' (nec) activity category contains activities that are infrequent or unanticipated.
This category is used when there is a response given, but:
This category is used for responses that are positively identified (ie the meaning and the intent are clear) but which clearly fall outside the scope of the classification/topic as defined in the standard.
This category is only used where a respondent has not given any response to the question asked, ie it is solely for non-response.
Aas, Dagfinn (1982). "Designs for large scale time use studies of the 24 hour day". In Z.Staikev (ed.) Its about time: Proceedings of the International Research Group on time budgets and social activities. Sofia, Bulgaria pp 17–53.