It is not clear what exactly you want to calculate about the year.
It is not calculated. It is the convention in Western Europe and other English speaking countries that the New Year begins on January 1.
You use the definition of "efficiency": you divide output power by input power. Both of these, of course, need to be measured or calculated.
area
by displacement...
energy is calculated in "jouls"
Calculated from the year 2010, the year of birth was 1992.
It is not calculated. It is the convention in Western Europe and other English speaking countries that the New Year begins on January 1.
calculated in 2010 the year of birth was 1981.
Calculated in 2010, the year of birth was 1920.
Calculated in 2010 the year of birth was 1979.
Calculated from 2010, the year of birth is 1934.
Calculated in 2010, the year of birth is 1989.
Calculated in 2010, the year of birth was 1986.
calculated in 2010 the year of birth was 1992.
Calculated from 2012 the year of birth is 1966.
If you are 30 and its 2012 you were born in the year of 1972
calculated in 2010, the year of birth was 1928.