The Fund assessed withdrawal liability requiring DISA to pay $652/month for 20 years. This amount was calculated pursuant to 29 U.S.C. § 1399(c)(1)(C)(1)(I), which provides that withdrawal liability shall be calculated based upon the employer’s average number of contribution base units for the highest “3 consecutive plan years” during the 10 years preceding the plan year in which the withdrawal occurred. As DISA had only been a contributing for two years, the Fund had initially calculated a zero for the third year.The Fund subsequently changed its interpretation of the statute and concluded that because the third year was a zero-hour year, only DISA’s two years of contributions should be averaged, without taking into account a zero-hour third year.