Basal body temperature (BBT) charting is such a great tool. Simply taking your temperature using a quality digital thermometer first thing in the morning upon waking and before doing ANYTHING (including getting up, eating/drinking, talking) can be such a powerful insight into the health of your body (metabolic rate, thyroid health and fertility/hormonal factors).
People often mistake BBT charting as only a means for ovulation prediction. This is far from the truth. Female BBT charting (whether vaginal or oral) can be a great indicator of the balance of hormones in both the follicular and luteal phases of the menstrual cycle. It can also give an insight into the environment of the uterus and how well the endometrium is shedding each month. On top of this, yes it can also indicate whether ovulation is happening every month and give an insight into whether sufficient progesterone is being released by the corpus luteum to sustain a pregnancy.
For men, BBT charting can also be reflective of sperm health. There are ideal BBTs for optimum sperm numbers and quality.