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ZERO SLOPE: A horizontal line in which the numerical value of the slope, calculated as the change in the variable on the vertical axis divided by a change in the variable on the horizontal axis, is zero. In other words, the Yaxis variable is fixed, or constant, for any and all values of the Xaxis variable.
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ARC ELASTICITY: The average elasticity for discrete changes in two variables. The distinguishing characteristic of arc elasticity is that percentage changes are calculated based on the average of initial and ending values of each variable, rather than initial values. Arc elasticity is generally calculated using the midpoint elasticity formula. The contrast to arc elasticity is point elasticity. For infinitesimally small changes in two variables, arc elasticity is the same as point elasticity. Arc elasticity is best considered the average elasticity over a range of values for a relation. Like any average, some values within the range are likely to be greater and some less. However, it provides a quick approximation of elasticity when more precise and sophisticated calculation techniques are not possible.Working Through an ExampleA Standard Demand Curve 

 The demand curve displayed to the right can be used to illustrate the measurement of arc elasticity using the midpoint elasticity formula. If the price declines from $12 to $8, the quantity demanded increases from 4 to 6, from point X to point Z. Using this midpoint formula (with price designated as P and quantity designated as Q) average price elasticity of demand is:midpoint elasticity  =  (Q[Z]  Q[X]) (Q[Z] + Q[X])/2  ÷  (P[Z]  P[X]) (P[Z] + P[X])/2 
midpoint elasticity  =  (6  4) (6 + 4)/2  ÷  (8  12) (8 + 12)/2  =  (2) (5)  ÷  (4) (10) 
midpoint elasticity  =  0.4  ÷  0.4  =  1.0 
Ignoring the minus sign, the price elasticity of demand over this segment of the demand curve from X to Z is 1.0.An Average ValueThis value of 1.0 is actually an average for the entire range between points X and Z. Precise estimates of point elasticity shows that the elasticity is 0.67 at point X and 1.5 at point Z. Moreover, the elasticity is different at each point on a straight line demand curve such as this one. The only point in which the elasticity is exactly equal to 1.0 is at point Y, the midpoint between X and Z.This last observation is worth emphasizing. The midpoint elasticity formula effectively estimates the point elasticity at the very midpoint of the overall segment. This means that the elasticity of any point on a demand curve (point elasticity) can be obtained by calculating the arc elasticity with the midpoint elasticity formula such that the desired point is dead center in the middle, the midpoint of the arc.
Recommended Citation:ARC ELASTICITY, AmosWEB Encyclonomic WEB*pedia, http://www.AmosWEB.com, AmosWEB LLC, 20002014. [Accessed: April 24, 2014]. Check Out These Related Terms...       Or For A Little Background...       And For Further Study...      
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State of the ECONOMY
Consumer Price Index W
February 2014
230.871
Up 1.0% in 12 months Source: B L S
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Today, you are likely to spend a great deal of time visiting every yard sale in a 30mile radius wanting to buy either an AC adapter that won't fry your computer or a case for your designer sunglasses. Be on the lookout for crowded shopping malls. Your Complete Scope
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The first paper currency used in North America was pasteboard playing cards "temporarily" authorized as money by the colonial governor of French Canada, awaiting "real money" from France.


"You have to find something that you love enough to be able to take risks, jump over the hurdles and break through the brick walls that are always going to be placed in front of you. If you don't have that kind of feeling for what it is you're doing, you'll stop at the first giant hurdle. "  George Lucas


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