Basal body temperature (BBT) is the body temperature at recorded when your body is on rest. This temperature chart is known as BBT chart. This temperature record can be used to know your ovulation period.
BBT is recorded immediately upon awakening in morning. Record your body temperature orally with digital thermometer with decimal points daily and make use of some chart. Record this for 2-3 periods and you can see little spikes (higher temperature ) in those special days.
You can also use this chart for ovulation blood test and to use ovulation detection kits. When your BBT have spikes then you can perform these test to make sure you ovulation.
Now days you can find BBT thermometer in market which will keep record and show you picks in your BBT or you can use some software chart for this.
Keep thermometer near to your bed and do first thing after awakening is recording of temperature and then do other things. Do not eat or drink any thing before measuring your BBT even do not drink water.