Bbt confusion !!!!!!'


Can somebody explain to me a little about how bbt works ?? From my previous understanding I thought ovulation day was the day after the temp dip ?? But ive since been told by a friend that you count the dip temp as ovulation day ?? I'm soooooo confused. Here is my current chart which FF has said I ovulated on the Sunday. Is this correct or is it the Monday like I thought 🤔🤔