** Updated with pictures **
Just for fun and for practice, I made an attempt to draw my first crotch curve last week. I used my 40" flexible ruler. I wrapped 3 individual rubber bands on the ruler. One to mark my front waistline, one to mark my crotch point, and the last one to mark my back waistline. I wrapped the ruler from my front, under my crotch, and over my rear. Yes, I had to wiggle the rubber bands along the flexible ruler for proper placement to represent the 3 points on my body. I carefully stepped out of my flexible ruler and immediately placed the ruler on my cutting table. I had already laid out and taped together 2 sheets of 8-1/2"x11" paper. I traced the inside edge of my ruler and marked the rubber band points on my paper.
Today, I plan on producing an accurate crotch curve. I will be using 1/4" elastic to wrap around my waist and using my flexible ruler to get an accurate crotch curve along with the 3 points (front waist, crotch pt, and back waist).
I plan on tracing my crotch curve on a piece of sturdy white paper and also on my tracing paper.
I also ordered a Pants Fitting book by Cynthia Guffey.
I will be back to post a picture of my crotch curve.
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I finally got around to producing a pretty accurate crotch curve and I have pictures to show.
First off, I couldn't find my white roll of paper. So, I ended up taking four (4) pieces of 8-1/2" x 11" paper and taping them together.
I put on my one-piece swimsuit and tied my 1/4" wide elastic around my waist. I stepped into my flexible ruler and made sure the "rubber bands" were hitting my front waist and crotch point. DH (who was laughing hysterically at this point) helped me adjust the back waist rubber band on the ruler to match the elastic at my back waist.
Once I explained to DH that this step was necessary for proper pants fitting, he quieted down considerably. We did have a good laugh.

I had just "stepped out" of my flexible ruler and quickly laid it on my white paper. I used my Crayola pencil to trace the curve inside the ruler. I marked a line where the rubber band points were. The "front" of the curve is on the left side near the pencils.

I decided to try 3 times and traced the 3 curves. As you can see, I came up with 3 slightly different results. I am going with the last traced curve I did, which is the inside curve. When I stepped out of my ruler, I had to be careful not to distort the ruler. I finally got the hang of it on my third try.

Here's a picture of one of the rubber bands "wrapped" around the ruler.
Guess what? My practice crotch curve from last week was pretty close to the one I drew this afternoon. I feel comfortable going forward with what I have.
Now, I have a question to my fellow sewists.
Does this crotch curve look weird to you? Average? What does it tell you?