Decimal Multiple and Sub multiple Factors and Guidelines for the application


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Decimal Multiple and Sub multiple Factors and Guidelines for the application

Since all the coherent units are not of a convenient size for all applications, provision had to be made for multiples and sub multiples of the coherent units. A complete list of such factors is given below .

*pronounced a s jeega

Note - The prefix factors greater than unity have Greek origin; those for factors less than unity have Latin origin

(except femto and atto, recently added, which have Danish origin).

 

  • Almost all abbreviations of prefix for magnitudes <1,are English lowercase letters. An exception is micro (Greek letter ).
  • Abbreviations of prefixes for magnitudes >1 are English uppercase letters. Exceptions are kilo, hecto and deca.
  • The prefixes hecto, deca, deci and centi should not be used unless there is a strongly felt need.

Guidelines

Guidelines for the application of these Prefixes are as follows:

 

  1. Multiples of the fundamental unit should be chosen in powers of +- 3n where n is an integer. Centimeter, owing to its established usage and its convenient size, cannot be given up lightly.

 

 

  1. Double or compound prefixes should be avoided, example, instead of micromicro farad (F), use picofarad (pF).

 

 

  1. To simplify calculations, attach the prefix to the numerator and not to the denominator. For example, use MN/m2 instead N/mm2  ; even though mathematically, both forms are equivalent.

 

  1. The rules for binding-in indices are not those of ordinary algebra, e.g., cm2 means (cm)2 = (0.01)2 m2  = 0.0001 m2, and not c * (m)2 = 0.01 m2.

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Other Accepted Units

It has been recognized at the international level, that some departures from strict purity and coherence are acceptable for practical reasons.  For instance, pure SI would acknowledge only decimal multiples and sub multiples  of the second for time measurement; whereas minute , hour, day, month and year are in everyday use internationally and will clearly continue to be used. Similarly,  the division of the circle into 360 degrees is an internationally recognized practice. Some symbols, ther than SI, that are commonly used to express physical quantities are given in the table below :

Name

Abbreviation

Name

Abbrev

angstrőm

Å

Inch

In

British thermal unit

Btu

Killowatt-hour

kW h

calorie

Cal

Mile

mi

day

d

Minute (of arc)

‘

degree

o

Minute (of time)

Min

dyne

dyn

pound

lb

electron volt

eV

revolution

rev

foot

ft

second (of arc)

“

gauss

G

standard atmosphere

atm

horsepower

hp

atomic mass unit

amu

hour

h

year

y