four buttons working

src/main/java/rocks/zipcode/calcskin/CalcSkin.java

@@ -182,7 +182,7 @@ public class CalcSkin extends Application {
         button.setOnAction(new EventHandler<ActionEvent>() {
             @Override
             public void handle(ActionEvent actionEvent) {
-                currentValue.set(Math.pow(currentValue.get(), 2));
+                currentValue.set(calcEngine.square(currentValue.get()));
             }
         });
     }
@@ -192,7 +192,7 @@ public class CalcSkin extends Application {
         button.setOnAction(new EventHandler<ActionEvent>() {
             @Override
             public void handle(ActionEvent actionEvent) {
-                currentValue.set(Math.sqrt(currentValue.get()));
+                currentValue.set(calcEngine.squareRoot(currentValue.get()));
             }
         });
     }