I found this:
Rule 16.2, Changing Course
This has now been restricted in its application so that in addition to rule 16.1, when after the starting signal a port-tack boat is keeping clear by sailing to pass astern of a starboard-tack boat, the starboard-tack boat shall not change course if as a result the port-tack boat would immediately need to change course to continue keeping clear. The rule therefore applies only upwind, to hunting by bearing away – the ‘dial-down’. The standard provisions of rule 16.1 cover hunting by luffing. Mike Hill