Why same thickness Lines in Grid show different thickness?

问题

I have a problem with line's thickness,And I can't figure out what's the reason. I have a stackPanel in which I put in 2 Grid.In each grid,I have two line with same thickness. Code is Here:

 <StackPanel Width="300" Margin="10" Height="200" VerticalAlignment="Top" Background="LightGray">
        <Grid>
            <Line X1="0" Y1="0" X2="200" Y2="0" Stroke="Red" StrokeThickness="1"/>
            <Line X1="0" Y1="24" X2="200" Y2="24" Stroke="Red" StrokeThickness="1"/>
        </Grid>
        <Grid>
            <Line X1="0" Y1="0" X2="200" Y2="0" Stroke="Red" StrokeThickness="1"/>
            <Line X1="0" Y1="24" X2="200" Y2="24" Stroke="Red" StrokeThickness="1"/>
        </Grid>
    </StackPanel>

and when I run the app, I found weird things like this: I'm wondering why the lines show different thickness.

来源：https://stackoverflow.com/questions/55338765/why-same-thickness-lines-in-grid-show-different-thickness