I don't know if this is what you are talking about, but somebody on another board posted it. I don't know if she's a member over here, though. If she is, hopefully she can elaborate more for us - it's really interesting!
http://www.cycletourist.com/biochart/
You enter your birthdate, month you want to target (e.g. when you conceived or hope to conceive) and ensure you include the correct time zone. You look at your o date to see where the emotion and physical lines connect on the chart.
To read the chart: a positive line is a line above the line and a negative line is below the center grid line.
* Girl = + Emotional Line (over line) and - Physical line (negative is under line)
* Lean Girl = both Emotional and Physical are negative at the target
* Boy = -negative Physical Line and -negative Emotional Line
* Neutral - as I understand it is when the lines are crossing the center of target date.
* Ideally both dh and you are in girl energy (ttc girl) or boy energy (ttc boy).
I did it for both of my boys & it was right for me. It was only right for dh on ds#1, though. It is kind of cool!