I bought this thermometer 2 years ago when I was trying to conceive and needed to have a more accurate reading of my basal temperature for my charts. It works exactly how it should.
First thing in the morning before talking, moving I would place it under my tongue and wait for around 30 seconds for it to beep, the temps were always very accurate in correlation to where I was in my cycle and ovulation was easy to pin point.
I just want to comment on a couple of the negative reviews. One lady said that if she repeatedly took her temp first thing in the morning it would change, so she decided to always use the last of 3 readings as her BBT. It doesn't work that way, your true basal temp has a magic window of about a minute before all your organs start waking up for the day increasing blood flow and therefore increasing your temperature. The first reading is always the most accurate.
Another lady said that if she left the thermometer in her mouth after the beeps it would keep increasing, the thermometer will beep when it reaches a plateau, so an increase from 37.16 to 37.18 isn't going to ruin anyones charting.
If it beeps and you notice a dramatic increase, the chances are it is not placed firmly enough under the tongue.
For the record, I loved this thermometer and I just pulled it out of the drawer this week after 2 years of non use so I could start charting again and it still works as it should.