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.
(p49). If you are an employee who received wages from an employer who did not withhold social security and Medicare tax from your wages, use Form 8919 to figure your share of the unreported tax. Include on line 58 the amount from line 13 of Form 8919. Include the amount from line 6 of Form 8919 on Form 1040, line 7.ther Taxes (p51). Use line 62 to report any taxes not reported elsewhere on your return or other schedules. To find out if you owe the tax, see the form or publication indicated. Enter on line 62 the total of all of the following taxes you owe.