Post-employment Benefits: Defined Benefit Plans :

Accounting for defined benefit plans is complex because actuarial assumptions are required to measure the obligation and the expense and there is a possibility of actuarial gains and losses. Moreover, the obligations are measured on a discounted basis because they may be settled many years after the employees render the related service. While the Standard requires that it is the  responsibility of the reporting enterprise to measure the obligations under the defined benefit plans, it is recognised that for doing so the enterprise would normally use the services of a qualified actuary