Marydel, Md., is really in Maryland, and its twin community of Marydel, Del., is really in Delaware. Which proves that Charles Mason and Jeremiah Dixon were right two centuries ago when they settled an argument between the Penns of Pennsylvania and Delaware and the Calverts of Maryland by surveying what came to be known as the Mason-Dixon Line.

In the 1950s, a resurvey was begun after the accuracy of Mason-Dixon was questioned, raising uncertainty whether the Eastern Shore border town of Marydel straddled the line--as local folks believed--or whether the Maryland portion actually belonged in Delaware.

Almost all the businesses are in Delaware, as are perhaps two-thirds of the roughly 250 residents. But the Maryland part is incorporated as a town in Caroline County, while the Delaware part is unincorporated. Such matters as taxation and political representation rested on the outcome.

A few days ago, after nearly three decades, the results of the resurvey by the U.S. Oceanic and Atmospheric Administration and the Maryland Geological Survey were announced. Mason and Dixon were accurate.

All this makes the local folks happy, according to Edgar Harman, manager of the U.L. Harman Inc. lumberyard, which straddles the line. "I can sit in a corner of the building and spread my legs and be in both states," he said.

In fact, Harman said, Marydel is unusual in having the same post office serve two states with separate zip codes: 21649 for Maryland, 19964 for Delaware. But the two communities are served by different telephone companies and exchanges. Harman said his firm has two numbers (Maryland area code 301, Delaware area code 302) and it costs 35 cents to call from one side of his switchboard to the other.