Select images for the Pie Medical interface

Open the interface and click on 'Toolbar On' in the menu. You'll see that the Pie selection tool has been assigned to the left mouse button.
Display the image you want to analyse using the scrollwheel or the scrollbar. Press the image with the left mouse button or, if you've assigned the Pie selection tool to the right mouse button, with the right. You'll see that the selected image appears in the Pie interface.
The red numbers displayed in the interface images are the image number and the sequence number in the overview window.