Yes, I've done that.. more than once. I've even plotted a graph from it! The problem for me is that these rates seem to change before my period, during my period, near the end of my period, a few days after my period, at ovulation!!! By the time I've worked out a good rate (or rates), it's changed again and I can't keep up with it! It even changes month to month- so I find a good rate for period, for example, and the following month it doesn't work. I'm chasing my tail and very very tired.