I've never seen or heard of anyone actually marking their vents like that. I don't. When I make notes like that, it's just an estimate from a quick look. Also, vent adjustments will vary wildly from smoker to smoker and even from cook to cook, based on things like how airtight your smoker is, the fuel you're using, how much food you're cooking, the outdoor temperature, wind, humidity, sun, shade, and such. This also means that you shouldn't rely too heavily on notes from someone else's log in deciding how to set your vents. My vent settings almost never match up with what I've seen in others' notes, with the exception that I think a lot of folks end up closing two of the three bottom vents completely and controlling the temps by adjusting one vent. I do this, unless I'm doing something at high heat and really need to open it up and let it rip. One of the nice things about smoking is that you can make some excellent BBQ without having to be all that precise. Close counts for a lot of the things we cook (with the possible exception of brisket), and you'll learn not to worry all that much about occasional temperature fluctuations of plus or minus 10 or 15 degrees.