When the model initially took the pose I measured the head and then used it to construct the rest of the drawing. This is a common practice and even though I have only recently started using this technique I use it to make sure that a) I will be able to fit the whole figure (or however much of it I want)onto the paper and b) that the proportion is generally accurate. In this case all this proceeded as planned until the model took a break and then resumed the pose. At this point, as anyone who is familiar with a life drawing session will know someone will often tell the model to move slightly to better match the original pose. In this case the model asked if every thing was alright and one person said, "Can you match my drawing?" which we all found humorous. (The model then replied, "No one has ever asked me to do that before!")
At that moment I looked at my drawing was about to say that the model's elbow was much too close to her hip when I realized that it was my drawing and not the pose that was off. I thought, "How could I have missed that? How could it be so far off without noticing until then?" I had measured the head, found the various places but had entirely missed an important relationship and continued to paint oblivious to my mistake. I did have the feeling that the figure was overly elongated, but I though that was because the head was too small so I had gone back and enlarged it before starting to paint.
As always we can only strive to do better next time, but this time I think I learned an important and I hope that I can remember it in the future.
As I do every session I did a second, quicker painting of the same pose which I will post tomorrow.