It works right out of the box. Start the OH1+, go to the Ambit3, Settings, Connect, HR-Belt. It will be found and can be used afterwards.
That’s what I thought. But upon starting a workout the watch displayed the HR only for one second and would just display blanks afterwards. Multiple re-connects of the OH1 did not solve the problem.
My problem was solved by a soft-reset of the Ambit3.
Dr. Hannes Steiner