Area is a measure of the square units of an enclosed 2 dimensional space:

Area of a circle =  where, r is the radius ( ½ the diameter) and

(3.1415926535897932384626433832795...)

e is the base of the natural system of logarithm, having a numerical value of approximately 2.718

Constants:

Avogadro's number = N = 6.02 x 1023	mass of earth = 5.98 x 1024 kg
speed of light = c = 3 x 108 m/s	earth equator radius =3960 mi = 6.38 x 106 m
density (mass / volume) of water = 1 g / cm3	acceleration of gravity =32 ft / s2 = 9.8 m / s2
distance to sun from earth = 93,000,000 miles	.. , e = 2.142..

Conversion Factors / Formulas:

Length	Volume	Energy	Mass
1 in = 2.54 cm	1 gallon = 3.7854 L	! J = 1 kg m2 / s2	1 oz = 28.3495 g
1 ft = 0.3048 m	1 quart = 0.946353 L	1 cal = 4.184 J	1 lb = 0.453592 kg
1 mi = 1.609344 km

Abbreviations:

Inch = in	Millimeter = min	Second = sec = s	Ounce = oz
Feet = ft	centimeter = cm	minute = min	pound = lb
yard = yd	meter = m	hour = hr	gram = g
mile = mi	kilometer = km	year = yr.	kilogram = kg
quart = qt	millimeter = ml	Joule = J	atmosphere = atm
gallon = gal	liter = L	calorie = cal	Coulomb = C
radian = rad	miles per hour = mi . Hr = mph	meter per second = m / sec = m /s	degree = deg = 0
feet per second = ft / sec = ft / s	revolutions per minutes = rev / min = RPM

Approximations / Others:

N0 = 1, e.g. 230 = 1

Math Models:

Linear Model

Exponential Model or   k = ln(1+r)

Logarithmic Model  y = ln x , e y =x,  x > 0

Absolute Value  | a | = a and | a | = -a Square Root Models