I did a temp experiment just to see if the bbt temp adjuster really work. I temp at 4:15am everyday I get up temp, record, and go back to sleep. On the weekends I do the same, but last weekend I took my temps at 4:15am and again at 7:15am, I put the 7:15 temp into the adjuster and it was accurate on both days for what my temp was at 4:15am. I know a lot of people are against BBT adjusting but if you ware waking up earlier or later it really can throw off your chart. The adjuster seems to work well if you have that problem.