This screenshot shows the layout in the alphanumeric trail which required the user to select the circles in the order A 1 B 2 ... K 11 L 12.

This resource can be downloaded or viewed using the link: tr_alnum_real.png

If you have wget available (typically on linux systems), then you can also obtain a copy using the command

 wget  -nd  biobank.ndph.ox.ac.uk/ukb/ukb/images/tr_alnum_real.png