A method and system of providing an adaptive reference orientation usable for determining a relative head orientation of a user, the method being implemented by a processing unit and comprising: repeatedly providing: receiving first data sensed by one or more sensors, said first data being indicative of a user's head orientation; obtaining a new adaptive reference orientation by moving a current adaptive reference orientation at least partly towards said indicated head orientation, by an amount which is varied at least partly in accordance with second data, said second data having been sensed by one or more sensors and being indicative of changes of a current frame of reference of the user; computing head orientation relative to said adaptive reference orientation; and using said new adaptive reference orientation as a current adaptive reference orientation for a next repeat of operations.