It's the same as why you wouldn't measure your weight in ounces, but neither would you weigh something very light in pounds - you want a convenient number which is easy to interpret. PC is short for parsec and it's a unit of measurement equal to 3,000,000,000,000,000,000 cm!
Take your annual covered earnings (the earnings on which you pay Social Security payroll taxes), multiply it by that year's index factor and you will obtain your indexed wage for each year you have worked. Next, add up all these indexed wages and divide them by 35 to determine your average wage.
You can total your Social Security tax paid by adding the amounts in box 4 of the W-2 you receive from each employer. For example, if each employer withheld $4,200, the total paid is $8,400. Then, subtract the annual limit from the total paid to find your overpayment. In this example, subtract $4,624.20 from $8,400.or example, in 2012, the Social Security tax applied to the first $110,100 of your earned income. You'd pay the same in Social Security taxes whether your wages that year were $110,100 or $1 million.