I use my handy dandy left hand measuring tool. its always attached to the end of my left arm so it never gets lost
I go 4 fingers down from the collar on the front, and just under the front collar impression on the backside of the shirt.
everyones fingers are different so I measured mine and the 4 fingers measure 3.5"
I also use my left hand to guage where to put left chest logos.
I put the middle knuckle on my pinky finger at the middle of the bottom edge of the collar, then place the graphic 4 fingers down, at the tip of my middle finger across (imaginary line)
that measures 4" over from center line
hope that helps, you can tape up on a shirt where the graphic should go then put your hand on the edge of the collar to figure out your own handy dandy left hand tool too. depending on your hand size placement is different!
oh, and sometimes with one-of a kind customer supplied v-necks, especially on a ladies (for anatomical reasons) I'll have them put the shirt on, and place a piece of masking tape where they want the left chest logo. Cause I don't wanna get it wrong by guessing how the shirt is going to stretch over her body. and I am usually surprised how far off the tape mark is from where I would have put the logo with the shirt flat on the press, just looks weird.
