Joining the blue cardigan

Following the knitting instruction, I am at the point where I should join the fronts and the back of the cardigan together... but I am not sure.  I check reference books, try the cardigan on, still I can't decide.  Then I have a light bulb moment. I found an old sweater that fits me perfectly and put it on my dress form.

Put the knitting on top of the sweater.

I can see the sides are too wide apart.  Now I am sure; I have not done enough.

 A few more rows later...the two sides are touching each other.  I can start knitting the body in one piece.