Moonstone, good luck with TTC in your forties - it's not for the faint-hearted. A couple of us on this bus are 43 and a lady in her late thirties got her bfp recently, so it can be done for the oldies! 
What is adenomyosis and why has a hysterectomy been suggested? Would you consider IVF using donor egg?
Cymon, when we ovulate the corpus luteum releases progesterone causing our basal body temperature to rise for the next two weeks until AF, when it plummets again (unless there is a pregnancy and AF doesn't appear). Fertility Friend pinpoints ovulation by various methods: a) a positive opk input by you (ovulation typically occurs 24-36 hours after an LH surge is detected b) your fertile cervical mucus (watery or egg white) and c) when a nadir (lowest temperature) is followed by three temperatures higher than the previous six.
Confusion arises for FF when people like Sparkly only ovulate up to 72 hours after their initial LH surge. Also, some women don't have the classic nadir of temperature on the day of ovulation itself. Furthermore, some ladies' progesterone rises so slowly in the first few days of ov that FF struggles to see the 'three over six' temps rule and will therefore occasionally give tentative crosshairs indicating ovulation may have occurred but will await further temps to clarify. It doesn't help FF's cause, either, when we input fertile cm after ovulation, as they think we have perhaps not ov'd yet (but they're stupid and don't know that fertile cm can be normal in some women's luteal phase).
The general rule of thumb, though, is that a woman will ovulate the day after her positive opk and that day (ovulation) will be characterised by a nadir (low dip) in temp followed by a sharp and sustained rise in temperatures. Here's the best example I have from my chart history..