That's an awesome booklet, thank you, the cartoons are wacky fun. :) It looks like it's Exercise 3 though, the labels are on the bottom. What I was actually doing is Chart 3 Exercise 3, but they look similar.
Just be careful before doing these. "Please Note: Many exercise physiologists consider the sit-up in the higher levels to be capable of causing spinal injury, and therefore unsuitable for an unsupervised program. As always, please consult your physician before attempting any exercise program."
I pay pretty close attention now days, but your warning is a good reminder. I stopped doing situps a long time ago, and stick with crunches, as situps were just uncomfortable.
I think a general "pay attention to your body's warning signs" is a good common sense rule.