It is very hard to tell if a crestie is gravid. One major reason is the skin on the underside is pretty thick, the other being the animals are well fed (fat). We check our animalís cages everyday when we know they are going to lay soon. When we see some dirt kicked all over the cage (from their nest box), we know they laid. Thatís all there is to it, just keep looking everyday.
Do not add calcium to their food everyday. Too much calcium can supposedly over calcify the eggshells, which makes it impossible for the animals to break out upon hatching. Instead offer powdered calcium in a dish 24/7. The female will lick from the dish when she needs it. Good Luck! -Mike