Step 4: Make calendar cover
Being as this is a winter gift and I live in a mountainous area I chose a ski scene from my favourite classic Windows game, Ski Free. Since the recipient of this calendar grew up programming on old Windows machines, I know he'll appreciate the theme. it's nerdy nostalgia.
I made mine by opening an image editing suite and creating a new canvas. Using the dimensions I took earlier to make the box for the tube matrix the canvas has to be large enough for the front and sides. The first picture a layer superimposed to show face dimension and the cut lines at the corners. I lined up the image with the box underneath by marking the corners with a bare tree, an image seldom used elsewhere in the image. Once the dimensions were set I made a circle the same exterior diameter as the cardboard tubes I used. Then I copied them to recreate the physical matrix I made. Numbers from 1-24 were randomly assigned to each circle. My extra 25th spot was numbered specifically for that location and then decorated with a large Yeti.
I have included a blank version of my Ski Free image, and a sized PDF you are free to download and use. The PDF can also be edited in some image suites (Photoshop, GIMP), this file has all the layers I used in creating my image.