Instruction(s) (as to a vessel’s navigation or movements)
When a VTS is authorized to issue instructions to vessels, these instructions should be result-oriented only.
The details of execution, such as course to be steered or engine manoeuvres to be executed should be left to the discretion of the master or pilot on board the vessel.
Source: IALA VTS Manual
Vessel Traffic Services
International Association of Marine Aids to Navigation and Lighthouse Authorities - AISM