Basal body temperature (BBT) method, where a person takes daily temperature checks to monitor their menstrual cycle. Beliefs about a slight drop in post-ovulation temperature, referred to as an implantation dip, could cause some to falsely believe they are pregnant. Basal body temperature, a person's lowest natural body temperature, responds to hormonal fluctuations throughout the menstrual cycle. Each cycle starts with resting eggs, a low estrogen level, and a baseline basal body temperature. As an egg grows and matures, it makes estrogen. Once a peak level of estrogen is reached, ovulation is triggered and the ovaries make progesterone. Progesterone will increase body temperature thus signifying ovulation. Consistency is a key factor in tracking ovulation. Readings should be taken at the same time every day, immediately upon waking, after several hours of consistent sleep. It should be measured before eating, drinking, or any other activity. A BBT thermometer, which is accurate to the 1/10th degree, should be used. The accuracy of the body temperature can also be affected by such variables as subtle environmental or lifestyle changes—such as interrupted sleep, changes in sleep patterns, alcohol consumption, emotional stress, infection, jet lag, and having recently stopping oral contraceptives. Implantation dip is a decrease in BBT by at least 0.3 degrees that occurs about a week after ovulation, roughly around the time of implantation, or the point at which a fertilized egg attaches itself to the wall of the uterus. However, there's no peer-reviewed evidence to support this. Basal body temperature, or BBT, may be able to tell a person when they are ovulating but it can be unreliable as various factors can impact it. There is also no concrete evidence that implantation dip, which occurs about a week after ovulation. Therefore, a more prudent method would be to utilize an ovulation predicator kit to better track ovulation.
Ref:
https://www.parents.com/getting-pregnant/ovulation/fertile-days/ovulation-pros-and-cons-of-ovulation-predictor-kits-opks/ 
