I bought the Polar F11 recently, and it said my VO~2~ max was 49 based on the fitness test. I got my VO~2~ max done last week professionally, and it was around 48, which means my watch was pretty accurate! Also, if you use your watch, make sure you pick your activity level accurately (I think there are 4 to choose from) because I chose low the first time and got 30 and then changed to high and got 48, which was the accurate one. (I did those two fitness tests at the same time.)

The professional test was fairly simple. I had to purchase a mask kit, which feels like wearing a gas mask, and then I walked/jogged on the treadmill. My test administrator increased the speed until 5mph and then gradually increased the incline by 2% until 10%. She was looking at a computer the whole time, so I'm guessing the computer told her or indicated to her when to increase the difficulty. I think it took around 8 minutes in total. It was very hard in the end, but I guess that's the point. The results of this test were very useful because they basically confirmed what I suspected for a long time: my zone is higher than the generic recommendations for heart rate. My zone 1 is 151-161 (73%-78% of max), and my zone 2 is 161-171 (78%-88%), and my anaerobic threshold was around 183 bpm (94%). I hope this helps.

I've attached my results so you can see an example. I had my body fat and resting metabolic rate done at the same time, so the first two pages are from that. The last 4 pages relate to the VO~2~ max testing.