With only 2 months of using the Ovacue monitor under my belt, I'm by no means a pro, but I've talked with Zetek about 5 times, and having had a "secondary fertility" situation in my 2nd month, I feel like I've got some good info and tips to offer anyone who might be interested...
In any case, forum leader Michaela has already given great info on how to use the monitor as far as oral and vaginal readings, etc., so I'll skip that and give other info with myself as an example (Michaela, since you have so much experience with other women's readings, feel free to edit anything I write that seems incorrect to you):
1) When you reach the time of predicted ovulation, watch for your own body signs as well, the ewcm, etc. At this point you're watching for a vaginal drop (Low reading) in your evening monitor test. When that happens, you've supposedly got about 12-36 hours before you'll ovulate. Mine apparently happens in about 12-18 hours, so I don't have much time. It's recommended that once you get that low, you use the vaginal monitor again the following morning after you've been up a couple hours, just to see if you're still low. That helps narrow down when ovulation occurs. Write down your reading, because you'll take the reading again that night at your normal time and it will wipe out the morning's reading. In my case, the mid-morning reading was still low, and I didn't realize the monitor's prediction of highest fertility (in my case, the 2nd) WOULD NOT CHANGE, so I was expecting to wait until then to TTC...
and that's where I was in error... the monitor continued to predict the 2nd as my highest fertility day, so I thought it was accurate. I've since learned that particular message does not change, it's a prediction! You MUST go by your vaginal low reading and watch for the rise for your timing, depending on what you're trying to sway for, or not! The monitor is right on in giving you your readings, and when ovulation attempts, but not necessarily when it actually does occur.
2) When the monitor adjusts for your readings and sees the actual rise, that's when you'll get the pink "ovulation confirmed" reading. For some women, that's accurate, but for others, if you have a longer cycle/later ovulation date than the average, or the first attempt doesn't work and your body tries again to ovulate, that message can be erroneous. I believe forum leader Michaela has had enough women coming to her in despair with questions to prove that one.
In my case, I got the lovely pink Ovulation confirmed message a day before my predicted "highest fertility" date, but 2 nights later I got the vaginal rise again and a purple Ovulation confirmed message, so I was one of those with a secondary fertility attempt. My colors did adjust, and my other messages changed as far as "highest, high, etc.), so I could see something was going on, but I didn't know what was happening. So just take your prediction with a grain of salt... it was right for me the first month, and right in between my first ovulation attempt and the second on my second month, but your readings and your body are the real indicators. I recommend continuing to use OPK tests and others also swear by temp charting (I guess if I get a BFN this month, I'll start that too.) That said, I do like the monitor so far, as it helps to see the colors and watch them along with the readings.