What is difference in number of crystalline water molecules in a molecule of gypsum and a molecule of Plaster of Paris?

The compound formed after heating is the plaster of Paris$(\mathit{CaS}{O}_4.1/2H_{2}O)$. It is made from Gypsum$(\mathit{CaS}{O}_4.2H_{2}O)$ on heating at the temperature of 373 K and changes back to gypsum by adding water to it. Plaster of Paris is used for setting fractured bones.
                     CaSO₄.2H₂O(Gypsum) $\to$ CaSO₄.1/2H₂O(Plaster of Paris) + 3/2H₂O

Hence, 3/2 is the difference in the number of crystalline water molecules in a molecule of gypsum and a molecule of Plaster of Paris.