Rule of Thumb – Procedure or Practice

Rule of Thumb is a procedure or practice which had been developed from experience and common understanding but it had nothing to do with technical or scientific knowledge. It had first been used in 1962 in English and the expression relates to the making of rough estimates of measurement with the use of the thumb, i.e. the distance to the first knuckle which was about an inch.

The origin of the phrase is not known and the earliest knowledge comes from J. Durham’s `Heaven upon Earth’, 1685, wherein he states `Many profess Christian are like foolish builder who build by guess and with the rule of thumb’.

The phrase also existed in various other languages and the plural form is rules of thumb. The phrase is presumed to have been originated with carpenters who utilised the width of their thumbs rather than rulers as a means of measurement for things, cementing its modern use though not precise, but reliable and convenient standards.

The rule of thumb as a unit of measure tends to appear also in Dutch where the word for thumb – duim also means inch and the use of a single word for inch and thumb seems to be common in many Indo European languages. Some examples are: in French: puce inch/thumb, Spanish: pulgada inch, pulgar thumb, Italian: pollice inch/thumb, Portuguese: polegada inch, polegar thumb: Swedish: tum inch, tumme thumb, Sanskrit: angulam inch, anguli finger etc.

Origin derived from Measurement 

Another possibility on the originof the phrase is derived from measurement especially in agricultural fields where the plant is in need of a precise depth to plant the seed properly and whether planted from seed or replanted, the depth was at times estimated with the use of the thumb, which was the rule of the thumb for measurement.

 As per Gary Martin, he states that `the origin of the phrase remain unknown and it is likely that it refers to one of the numerous ways that thumbs have been used to estimate things, judging the alignment of distance of an object by holding the thumb in one’s eye-line, the temperature of brew, measurement of an inch from the joint to the nail to the tip or across the thumb etc.’

He further adds that the phrase joins the whole nine yards as one that probably derives from some form of measurement but which is unlikely ever to be definitively pinned down’.

Financial Rule of Thumb

Yet another version on the phrase `rule of thumb’, is that the coarseness of flour ground, produced by grist mills in Old England, would be assessed when rubbed between the thumb and forefinger by the miller.

The rule of thumb typically developed out of practice and experience instead of the scientific theory or research and investors may find it familiar with a number of financial rules of thumb which may be intended, enabling them to learn, remember whereby they can apply financial guideline inclusive of those that address procedures and methods enabling them to save and invest which would be helpful for retirement.

Though the rule of thumb could be appropriate for a wide audience, it may not be applicable universally to all individuals and unique set of circumstances.