The Grade 439 Extra Thin Extra is marked Extra on the movement it is a 21J movement just like the 438 and there is an obvious parallel between the 538 Illini and the 539 Illini Extra with the 438 Extra Thin and the 439 Extra Thin Extra. There is one example in the collection and with serial number 3904929 and total production of 330, similar to the 539. This example is in a nice gold case with a fancy dial and would have been one of Illinois more expensive products when sold. It may have been more expensive than any of the railroad watches. With no cap in the case it would not have been Illinois most expensive watch.