Yesterday I carefully cleaned the CRTs and mirror. However, when I had to roll back my set, the set took a slight "bump" as the wheel of the TV moved into the groove of the carpet. I checked convergence and it looked pretty. I know my ISF calibrator said he tighted the bolts well on the CRTs when he adjusted for focus a couple of months ago. My question is, how sensitive is focus? Can it get knocked out of place easy?