In other words, a woman with a 40-day cycle
would ovulate on day 26, a woman with
a 30-day cycle
would ovulate on day 16, a woman with
a 31-day cycle would ovulate on day 17, etc. This was a surprise to me, but one of the MedHelp doctors wrote it up, I think you could find her post about it here on the site to see if it sounds right. The variation in length of cycle is apparently all at the front end, the follicular phase, not in the luteal phase.
"7 weeks one day ....