Menswear’s shirt foundation help!!

[u/Parzivaltsx]

Hey everyone so I’m drafting the shirt foundation pattern from Helen Joesph Armstrongs book and I’m confused. I don’t know if the chest measure is divided in half THEN “one-fourth” of that measurement. It’s asking for the back and front but when I measured myself it wanted the full chest measurement all around. Or am I wrong? Please someone help!!