A second set of changes, completed in 1993, has lowered the maximum salary used to calculate future pensions to $150,000.
The multinational oil giant BP Amoco plans to adjust the way it calculates pensions for its British retirees.
The discount rate, which translates the value of future payments into today's dollars, is one of the most powerful assumptions used in calculating pensions.
Tenneco, in calculating pensions, multiplies its employees' compensation by the number of years they have worked at the company.
It would give teachers retiring before July 1 credit for three extra years of service in calculating pensions.
If the Senate bill becomes law, the new way of calculating pensions would stay in force for two years.
Companies have been particularly hostile to the idea of calculating pensions on the basis of a yield curve.
Union officials said, however, that the higher percentage would still be used for calculating pensions and future increases.
As ever, women get less than their fair share when it comes to calculating pensions.
More than 3, 000 people do not get their rightful pension in time because the authorities are unable to calculate pensions when people have worked in other countries.