I turned the book to face the ceiling light in the room. No phone required, just a line of light from the "light source" icon" to your gnomon of choice.
i just roughed it out and guessed a couple times. Just take the pencil and lay it on the light source and the pencil mark. It should get you the results.
The shadows fall over several numbers. Even tried drawing the shadow paths based on the position of the light an the pencil but same results.Tried various combinations. None worked. How to determine which number to use? .