diff --git a/javafx-template/src/main/java/app/App.java b/javafx-template/src/main/java/app/App.java
index 17d788e..bbe9412 100644
--- a/javafx-template/src/main/java/app/App.java
+++ b/javafx-template/src/main/java/app/App.java
@@ -1,4 +1,4 @@
-package groupid;
+package app;
 
 import javafx.application.Application;
 import javafx.fxml.FXMLLoader;
diff --git a/javafx-template/src/main/java/app/AppController.java b/javafx-template/src/main/java/app/AppController.java
index 348e0f6..ab72ff9 100644
--- a/javafx-template/src/main/java/app/AppController.java
+++ b/javafx-template/src/main/java/app/AppController.java
@@ -1,11 +1,136 @@
-package groupid;
+package app;
 
-import java.io.IOException;
+import java.util.List;
+import java.util.function.BinaryOperator;
+
+import javafx.event.ActionEvent;
 import javafx.fxml.FXML;
+import javafx.scene.control.Label;
+import javafx.scene.control.Labeled;
+import javafx.scene.control.ListView;
 
 public class AppController {
 
+    private Calc calc;
+
+    public AppController() {
+        calc = new Calc(0.0, 0.0, 0.0);
+    }
+
     @FXML
-    private void switchToSecondary() throws IOException {
+    private ListView<Double> operandsView;
+
+    @FXML
+    private Label operandView;
+
+    @FXML
+    void initialize() {
+        updateOperandsView();
+    }
+
+    private int minOperandCount = 2;
+
+    private void updateOperandsView() {
+        while (calc.getOperandCount() < minOperandCount) {
+            calc.pushOperand(calc.getOperandCount(), 0.0);
+        }
+        List<Double> operands = operandsView.getItems();
+        operands.clear();
+        for (int i = 0; i < minOperandCount; i++) {
+            operands.add(calc.peekOperand(minOperandCount - i - 1));
+        }
+    }
+
+    private String getOperandString() {
+        return operandView.getText();
+    }
+
+    private boolean hasOperand() {
+        return ! getOperandString().isBlank();
+    }
+
+    private double getOperand() {
+        return Double.valueOf(operandView.getText());
+    }
+    
+    private void setOperand(String operandString) {
+        operandView.setText(operandString);
+    }
+
+    private void setOperand(double d) {
+        setOperand(Double.toString(d));
+    }
+
+    private void clearOperand() {
+        setOperand("");
+    }    
+
+    @FXML
+    void handleEnter() {
+        if (hasOperand()) {
+            calc.pushOperand(getOperand());
+        } else {
+            calc.dup();
+        }    
+        clearOperand();
+        updateOperandsView();
+    }    
+
+    private void appendToOperand(String s) {
+        setOperand(operandView.getText() + s);
+    }
+
+    @FXML
+    void handleDigit(ActionEvent ae) {
+        if (ae.getSource() instanceof Labeled l) {
+            appendToOperand(l.getText());
+        }
+    }
+
+    @FXML
+    void handlePoint() {
+        var operandString = getOperandString();
+        if (operandString.contains(".")) {
+            setOperand(operandString.substring(operandString.indexOf(".") + 1));
+        } else {
+            appendToOperand(".");
+        }
+    }
+
+    private void performOperation(boolean swap, BinaryOperator<Double> op) {
+        if (hasOperand()) {
+            calc.pushOperand(getOperand());
+            clearOperand();
+        }
+        if (swap) {
+            calc.swap();
+        }
+        calc.performOperation(op);
+        updateOperandsView();
+    }
+
+    @FXML
+    void handlePi() {
+        setOperand(Math.PI);
+    }
+
+    @FXML
+    void handleOpAdd() {
+        performOperation(false, (op1, op2) -> op1 + op2);
+    }
+
+    @FXML
+    void handleOpSub() {
+        performOperation(true, (op1, op2) -> op1 - op2);
+    }
+
+    @FXML
+    void handleOpMult() {
+        performOperation(false, (op1, op2) -> op1 * op2);
+    }
+
+    @FXML
+    void handleOpDiv() {
+        performOperation(true, (op1, op2) -> op1 / op2);
     }
 }
diff --git a/javafx-template/src/main/java/app/Calc.java b/javafx-template/src/main/java/app/Calc.java
new file mode 100644
index 0000000..7200359
--- /dev/null
+++ b/javafx-template/src/main/java/app/Calc.java
@@ -0,0 +1,69 @@
+package app;
+
+import java.util.ArrayList;
+import java.util.List;
+import java.util.function.BinaryOperator;
+import java.util.function.UnaryOperator;
+
+public class Calc {
+    
+    private List<Double> operandStack = new ArrayList<>();
+
+    public Calc(Double... operands) {
+        operandStack.addAll(List.of(operands));
+    }
+
+    public int getOperandCount() {
+        return operandStack.size();
+    }
+
+    public void pushOperand(int n, double d) {
+        operandStack.add(operandStack.size() - n, d);
+    }
+
+    public void pushOperand(double d) {
+        pushOperand(0, d);
+    }
+
+    public double peekOperand(int n) {
+        return operandStack.get(operandStack.size() - n - 1);
+    }
+
+    public double peekOperand() {
+        return peekOperand(0);
+    }
+
+    public double popOperand(int n) {
+        return operandStack.remove(operandStack.size() - n - 1);
+    }
+
+    public double popOperand() {
+        return popOperand(0);
+    }
+
+    public double performOperation(UnaryOperator<Double> op) {
+        var op1 = popOperand();
+        var result = op.apply(op1);
+        pushOperand(result);
+        return result;
+    }
+
+    public double performOperation(BinaryOperator<Double> op) {
+        var op1 = popOperand();
+        var op2 = popOperand();
+        var result = op.apply(op1, op2);
+        pushOperand(result);
+        return result;
+    }
+
+    public void swap() {
+        var op1 = popOperand();
+        var op2 = popOperand();
+        pushOperand(op1);
+        pushOperand(op2);
+    }
+
+    public void dup() {
+        pushOperand(peekOperand());
+    }
+}
\ No newline at end of file
diff --git a/javafx-template/src/main/resources/app/App.fxml b/javafx-template/src/main/resources/app/App.fxml
index b0e6c58..d9b4203 100644
--- a/javafx-template/src/main/resources/app/App.fxml
+++ b/javafx-template/src/main/resources/app/App.fxml
@@ -1,16 +1,52 @@
 <?xml version="1.0" encoding="UTF-8"?>
 
-<?import javafx.scene.layout.VBox?>
+<?import javafx.scene.layout.GridPane?>
 <?import javafx.scene.control.Label?>
 <?import javafx.scene.control.Button?>
-<?import javafx.geometry.Insets?>
+<?import javafx.scene.control.ListView?>
 
-<VBox alignment="CENTER" spacing="20.0" xmlns="http://javafx.com/javafx/8.0.171" xmlns:fx="http://javafx.com/fxml/1" fx:controller="app.AppController">
-   <children>
-      <Label text="Primary View" />
-      <Button fx:id="primaryButton" text="Switch to Secondary View" onAction="#switchToSecondary"/>
-   </children>
-   <padding>
-      <Insets bottom="20.0" left="20.0" right="20.0" top="20.0" />
-   </padding>
-</VBox>
+<GridPane xmlns="http://javafx.com/javafx/8.0.171" xmlns:fx="http://javafx.com/fxml/1" fx:controller="app.AppController"
+         alignment="CENTER" hgap="10.0" vgap="10.0" >
+
+   <ListView fx:id="operandsView" prefHeight="80.0"
+      GridPane.rowIndex="0" GridPane.columnIndex="0" GridPane.columnSpan="4"/>
+   <Label text="" fx:id="operandView"
+      GridPane.rowIndex="1" GridPane.columnIndex="0" GridPane.columnSpan="4"/>
+
+   <Button text="E&#10;n&#10;t&#10;e&#10;r" onAction="#handleEnter"
+      GridPane.rowIndex="2" GridPane.columnIndex="3" GridPane.rowSpan="4"/>
+
+   <Button text="7" onAction="#handleDigit"
+      GridPane.rowIndex="2" GridPane.columnIndex="0"/>
+   <Button text="8" onAction="#handleDigit"
+      GridPane.rowIndex="2" GridPane.columnIndex="1"/>
+   <Button text="9" onAction="#handleDigit"
+      GridPane.rowIndex="2" GridPane.columnIndex="2"/>
+   <Button text="4" onAction="#handleDigit"
+      GridPane.rowIndex="3" GridPane.columnIndex="0"/>
+   <Button text="5" onAction="#handleDigit"
+      GridPane.rowIndex="3" GridPane.columnIndex="1"/>
+   <Button text="6" onAction="#handleDigit"
+      GridPane.rowIndex="3" GridPane.columnIndex="2"/>
+   <Button text="1" onAction="#handleDigit"
+      GridPane.rowIndex="4" GridPane.columnIndex="0"/>
+   <Button text="2" onAction="#handleDigit"
+      GridPane.rowIndex="4" GridPane.columnIndex="1"/>
+   <Button text="3" onAction="#handleDigit"
+      GridPane.rowIndex="4" GridPane.columnIndex="2"/>
+   <Button text="0" onAction="#handleDigit"
+      GridPane.rowIndex="5" GridPane.columnIndex="0"/>
+   <Button text="." onAction="#handlePoint"
+      GridPane.rowIndex="5" GridPane.columnIndex="1"/>
+   <Button text="π" onAction="#handlePi"
+      GridPane.rowIndex="5" GridPane.columnIndex="2"/>
+
+   <Button text="+" onAction="#handleOpAdd"
+      GridPane.rowIndex="6" GridPane.columnIndex="0"/>
+   <Button text="-" onAction="#handleOpSub"
+      GridPane.rowIndex="6" GridPane.columnIndex="1"/>
+   <Button text="*" onAction="#handleOpMult"
+      GridPane.rowIndex="6" GridPane.columnIndex="2"/>
+   <Button text="/" onAction="#handleOpDiv"
+      GridPane.rowIndex="6" GridPane.columnIndex="3"/>
+</GridPane>