What Does Width Mean In G++

The code below produced the image under it.As you can see the code always uses 10 for the width.But the squares and lines are not all the same width.Are there some rules I can follow or do I have to simply cut-and try to get a desired width?How does DrawRectangle treat a pen with an even number for width?Likewise, an odd number?Is that true for Circles and polygons?

gr.DrawString(e.Graphics.PageUnit.ToString, New Font("Ariel", 10), Brushes.Red, 30, 0)
gr.DrawRectangle(New Pen(Color.Yellow, 1), 10, 10, 10, 10)
gr.FillRectangle(New SolidBrush(Color.Yellow), 10, 30, 10, 10)

[code]....