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.
To earn the maximum benefit, you must have made at least the maximum taxable amount of wages every year of your working life since the age of 21. In 2012, that amount was set at $110,100. If you earn any wages over and above that amount, you did not pay Social Security taxes on the earnings. Making an Adjustment If you're curious about your entitlement to retirement benefits, you can request a Benefit Statement by going online at ssa.gov or calling the agency as 800-772-1213.