Joe Anderson traveled to Farnborough in 1978 to experience the Harrier and the Ski Jump with the chief Harrier test pilot, John Farley. This particular ramp was 15 degrees. Various angles were tested. The final ramp angle used on several ships was 12 degrees as a compromise between takeoff performance and shock loads on the nose landing gear.
Notice the excellent weather! Joe reported they were in the clouds by 400 feet!