I tweaked my RPTV's convergence last January - it was as close to perfect as possible (using Avia crosshatch at 100 IRE). Last night - four months later - while the convergence still looks pretty good - it had clearly changed. Is this normal? My TV is just over three years old. I am going to tweak it this weekend. Using the "fine" mode works. Also, My TV was ISF'd about a year and half ago - How often is it necessary?