CREATE TABLE table_68273 ("Unit" TEXT, "Type" TEXT, "Gross MW" TEXT, "Construction start" TEXT, "Operation start" TEXT)

Construction start of 1 december 1984 is what unit?
SELECT "Unit" FROM table_68273 WHERE "Construction start" = '1 december 1984'
SELECT "Unit" FROM "table_68273" WHERE "Construction start" = '1 december 1984'