extra 4 buttons

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

         screen.setStyle("-fx-background-color: red;");
         screen.setAlignment(Pos.CENTER_RIGHT);
         screen.setEditable(false);
-        screen.textProperty().bind(Bindings.format("%.0f", currentValue));
+        screen.textProperty().bind(Bindings.format("%.4f", currentValue));
         return screen;
     }
 
                 makeSquareButton(button);
             } else if ("√x".equals(s)) {
                 makeRootButton(button);
-            } else if ("1/x".equals(button)){
+            } else if ("1/x".equals(s)){
                 makeInverseButton(button);
             }
         }