Answer: RULEOFTHUMB

AnswerCrossword Clue
RULEOFTHUMBGeneral guideline
RULEOFTHUMBGeneral principle
RULEOFTHUMBPractical method of procedure
RULEOFTHUMBNonscientific gauge
RULEOFTHUMBUnscientific procedure
RULEOFTHUMBHitchhikers' code?
RULEOFTHUMBCommon sense procedure
RULEOFTHUMBWidely applied principle