I have always used the rectangle tool to draw a box, gone up on the menu bar and used the W and H dimension boxes to set it to the correct dimensions. Now, those are not staying as I put them when I hit enter. They may be only .006 off, but they are not exact. So I used the rectangle tool, clicked on my page and put the dimensions in the box that appears. When I click OK, the dimensions above show the same discrepancies.
I am using CS4.