Support the one severe event in 10,000 hours theory (one in 12,000 for me).That was going into Hannover on one of those rare occasions when a super cell formed over Europe (isol cb was the forecast)!! All airfields within 50 miles were closed.CAT prevented us reading instruments..the dirt from the floor was on the roof...then in your hair. Without the inertia reel lock would have needed the bone dome someone mentioned earlier. Had to get the aircraft checked to make sure we had not exceeded any limits.
Not long after this I came across the met definitions of turbulence and they referred to pitch attitiude, airspeed fluctuations , height changes etc for each. Don't remember where I found it.If can help you please post it because I too have had many guys and girls confusing no sig turb with moderate and light with severe.