Roman Diaz Unicorn step 42-47

[arnolasvegas]

I'm completely stuck with step 42 to 47 for the Unicorn by Roman Diaz.
Can anybody light me about it ?
Please make it simple... I have absolutely no idea of what I'm supposed to do with this X reference point.
I just see that it is inside at step 42 and outside at step 47, but I just don't understand those steps.
Please help me !!!

Thanks