CREATE TABLE table_204_959 (id NUMBER, "club" CLOB, "founded" NUMBER, "nickname" CLOB, "location" CLOB, "home ground" CLOB, "entered competition" NUMBER, "most recent promotion" NUMBER)

what is the difference , in years , between the founding of the heidelberg football club and the eltham football club ?
SELECT ABS((SELECT "founded" FROM table_204_959 WHERE "club" = 'heidelberg football club') - (SELECT "founded" FROM table_204_959 WHERE "club" = 'eltham football club'))
SELECT ABS((SELECT "founded" FROM "table_204_959" WHERE "club" = 'heidelberg football club') - (SELECT "founded" FROM "table_204_959" WHERE "club" = 'eltham football club'))