Answer: ruleofthumb

AnswerCrossword Clue
RULEOFTHUMB

General guideline

RULEOFTHUMB

General principle

RULEOFTHUMB

Practical method of procedure

RULEOFTHUMB
Nonscientific gauge
RULEOFTHUMB
Unscientific procedure
RULEOFTHUMBHitchhikers' code?
RULEOFTHUMBCommon sense procedure
RULEOFTHUMBWidely applied principle