I have used this little bug to set up my recording room where I practice acoustic guitar/vocals several hours a day. I was treating a room with sound deadening/sound absorbing materials and wanted to get comparative readings inside and outside the room and at various other points related to the room. This device has been incredibly handy in this process. (I can't speak to accuracy as I don't have any professionally calibrated devices to compare it to. However, I can say that all the readings I got were right in the ranges I was expecting, which is what the Makes device very accurate. . ) This little gauge is VERY sensitive in a good way. When you turn it on for the first time, you'll have to give it a few seconds to normalize because, as you'd expect, the initial sound pressure reading is unstable until the unit returns to normal. A really good example of sensitivity - I live a good 200 meters from a service road - when I'm sitting in my fairly soundproof new building and the car drives that far I see a brief slight rise in dB and then it goes down again. At first I thought it was a coincidence, but I noticed that this happens all the time. When a motorcycle or small truck drives by I see a similar rise and then fall in readings - which I expected - the car was unexpected as it was (to me at least) barely audible. My point is that this device is extremely sensitive (for such a cheap device) and users should be aware that deviations in readings are to be expected with even the slightest noise. I also find that the (rather loud) ticking of the clock hanging on my walls causes vibration. All in all a great device! The price was amazing, personally I think it's well made and as I said it's very responsive in a good way. Documentation is useless, but there is nowhere easier. I didn't even want to try the Max/Min button in my app, but as other reviewers have pointed out, the documentation doesn't explain it. If you want to use this feature, just press the Max/Min button and see what it does. As for me, I was able to control the on/off (LOL) button very easily, and after the device went back to normal for a few seconds, I saw exactly what I needed to see - relative readings throughout the tone room setup! I would buy it again - no regrets - only positive things to say (documentation aside - but most users probably won't need documentation to work with a device that has an on/off switch and a different max/min function.) Oh I like the built in tripod nut - it can be useful in some cases. I'm also not sure why the specs say 40db to 130db - mine dates back to my teens and 20's in VERY quiet environments. Haven't felt like testing the upper class yet - maybe a trip to the airport or bike shop nearby would work!