Definitions.
(a) The word “whistle” means any sound signalling appliance capable of producing the prescribed blasts and which complies with the specifications in Annex III to these Regulations.
(b) The term “short blast” means a blast of about one second’s duration.
(c) The term “prolonged blast” means a blast from four to six seconds’ duration.
All whistle signals prescribed in the Rules, are specified in terms of short and prolonged blasts, so it useful to learn their respective definitions.