How do biorhythm charts work???

I have read a number of postings that swear by gender prediction using biorhythms.  I clicked on one of the recommended links and could not figure out how to make sense of the chart.  Can anyone explain how to read them to determine gender?

I used: www.cycletourist.com/biochart/

Thanks very much!

they were right for my sons...they were sway boy blue and red line in positive...this one was sway boy but I had swayed for girl...it was wrong due to my swaying... 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! Katie (35) DH (3

check the kits calendars section there is explanation there what the lines mean