A movement is afoot to require public pension plans to calculate and publish their market value of liabilities, a figure akin to a plan's termination liability. MVL is determined by using a) a "risk-free" rate of investment return--generally around four to five percent--to discount liabilities, rather than a return based on a diversified portfolio, which is 7.5 percent to 8.5 percent for most public pension plans; and b) the accumulated benefit obligation, which accounts for liabilities accrued to-date, rather than the pension benefit obligation, which projects future service and salary growth.  Corporate pension plans are required to calculate a MVL, chiefly so that in the case of bankruptcy or sale of the firm, the plan's liabilities are known. The Governmental Accounting Standards Board is studying the issue of how public pension liabilities are calculated and disclosed, as mandated in its Statements 25 and 27. Possible changes to these standards may include elements of MVL.