We are told to check our mezuzos twice every seven years. What exactly does this mean? If the Chachamim/Poskim had meant once every 3.5 years, would they not have said this instead?
With regard to tashmish ha-mitah, I was told "twice a week" means that there should not be a seven-day period without two episodes. Does this mean the same thing, namely that there should not be a seven-year period without two checkings, which seems to boil down to approximately every six years?