Using the thumb and forefinger approach will be tricky due to the lack of definitive features within the contour. The best approach is to measure the difference of the mass of the pelvic and lower abdominal area with the legs. A major feature to look for is the change in the directions at the top. Keep an eye out for the distinct top. And similar to Walter, the tilt of the center axis is critical.
The legs provide a good opportunity to explore the proportions for the design interpretation.
To reiterate:
One drawing will be the legs based on the observational measuring methods
One drawing will be based on visual observation but without an emphasis on using observational measuring methods. Draw while looking, but only adjust based on how you like the effect.