Use the tape measure and a marker to measure the length of the horizontal shelf and the vertical dividers. The shelf will be the length of the diameter of the circular base, which in our case is 600mm. Make the dividers half that length, minus the width of the ply. In our case the top divider is 287mm from the horizontal to the frame edge and the bottom divider is 273mm. Once you have measured the horizontal shelf and supports, put on your safety equipment and use the jigsaw or drop saw to cut them out.