SI system is based on seven basic, independent units, one of them, "meter" for length is also used to find unit for mass (1 cubic meter contains 1000 kgs of water).
The unit "meter" has no fundamental justification. Its hard to approximate for a layman what a meter is. There is another unit called "zira" which is far more understandable and easy. Infact, "zira" is the unit of length which is the first unit of anything ever used in any human civilization. For example, egyptians built pyramids using this unit, greeks used it extensively and so did romans. Perhaps great wall of china is also built using "zira" as a measuring ideal.
So, whats so special in "zira"? It is that one zira is equal to distance between the tip of middle finger and elbow of a man. Ofcourse that varies with height of people but still its an easy approximate that can be taught to a layman. Ofcourse zira has a specific length which do not vary with the peron using it, it is about 50 cm or 20 inches. Note that a person's height is equal to four time the distance between his middle finger and elbow (lets call that distance one "hand"). Therefore, a 6 ft tall man has one hand equal to 18 inches or 45 cm. It means that for a 10 inches hand the person's height need to be 80 inches or 6 ft 8 inches. Since almost all men are under that height (the exceptio would be less than 5% of population) so for almost every person his one hand is somewhat less than one zira.
The level of variation is like +/- 33% because men's heights vary between 5 ft and 8 ft 4 inches in different races. The 33% seems like a lot but atleast a person has a general idea of what a zira is, such an idea is totally absent for a meter.
Note that romans called zira a cubet and so do english speakers, although a cubet is now considered as 18 inches. That variation may be because romans standardized it for a 6 ft tall man's hand.
No comments:
Post a Comment