Hi, I've just started learning WPF, and followed a book to make this sample calculator application in XAML. The XAML code is attached below. I don't have any UI specific code in the xaml.cs file. However, I'm seeing a difference between design time and runtime. As you can see in the attached screenshot, the upper left button of the calculator is bigger than the rest. Even more confusingly, the designer when I edit the XAML shows the button correctly. I've tried to determine why is that, and I'm stumped. Can anyone help? I'm using VS2008, targeting framework 3.5, if it's any help. Here's the XAML: <TextBlock Grid.Row="0" Grid.Column="0" Grid.ColumnSpan="4" FontSize="24" Name="Header" VerticalAlignment="Center" HorizontalAlignment="Center">Calculator</TextBlock> <TextBox Grid.ColumnSpan="4" Grid.Column="0" Grid.Row="1" Name="Display" HorizontalContentAlignment="Left" Margin="5" /> <Button Grid.Row="2" Grid.Column="0" Click="Button_Click">7</Button> <Button Grid.Row="2" Grid.Column="1" Click="Button_Click">8</Button> <Button Grid.Row="2" Grid.Column="2" Click="Button_Click">9</Button> <Button Grid.Row="3" Grid.Column="0" Click="Button_Click">4</Button> <Button Grid.Row="3" Grid.Column="1" Click="Button_Click">5</Button> <Button Grid.Column="2" Grid.Row="3" Click="Button_Click">6</Button> <Button Grid.Row="4" Grid.Column="0" Click="Button_Click">1</Button> <Button Grid.Row="4" Grid.Column="1" Click="Button_Click">2</Button> <Button Grid.Row="4" Grid.Column="2" Click="Button_Click">3</Button> <Button Grid.Row="5" Grid.Column="0" Click="Button_Click">0</Button> <Button Grid.Row="5" Grid.Column="3" Tag="{x:Static local:Operation.PLUS}" Click="Op_Click">+</Button> <Button Grid.Row="4" Grid.Column="3" Tag="{x:Static local:Operation.MINUS}" Click="Op_Click">-</Button> <Button Grid.Row="3" Grid.Column="3" Tag="{x:Static local:Operation.TIMES}" Click="Op_Click">*</Button> <Button Grid.Row="2" Grid.Column="3" Tag="{x:Static local:Operation.DIVIDE}" Click="Op_Click">/</Button> <Button Grid.Row="5" Grid.Column="1" >.</Button> <Button Grid.Row="5" Grid.Column="2" Tag="{x:Static local:Operation.EQUALS}" Click="Op_Click">=</Button> </Grid>