Had awful turbulence over the French Alpes with a thunderstorm underneath us. Meal suspended, evrybody including Cabin Crew locked down. Went on for 20 mins, banging everywhere, Monarch A.300. I have always, as someone else said,used this as a yardstick to judge turbulence. Despite many screams from pax, aircraft held together, and have flown many times since, with passengers screaming at tiny bumps in comparison with this. Don't worry folks, it isn't going to break!!!, and wings are meant to waggle in turbulence!!!