I used to struggle with measuring out a specific amount, depending on what I had for boxes on each hive. Doing a stickyboard, etcetera... Watching researchers DUMP large quantities of Oxalic Acid Vapor into hives, every day for three to four MONTHS.... changed my mind.
At times, when I measured out an.... "Exacting" Amount of Oxalic Acid. I felt like I wasn't giving enough, sometimes I didn't get a good drop on the sticky board, and so had to do it again... I gave all that up...
I fill the pan of my Varrox Vaporizer, scrape it off level, and use it... I run it two minutes. Pull it out, dunk it in cold water, refill the pan, put it in the next hive, run it two minutes. and so on... I get a fantastic drop, the bees are minimally bothered, and I FEEL like I have accomplished something without wondering if it was enough. I know it was enough. Probably a bit too much. But I have yet to see or read about any side effects, or immunity/resistance to OAV.. even though many countries have been using it coming up on 30 years. It is still just as effective today as when they started.
I often see people saying they use other methods, to help prevent immunities from developing... I personally feel like, if immunities DO start developing, were going to start hearing about it from those people who have been using OAV for more than 20 years before we started using it over here. At least I HOPE we do, so we can take preventative measures, and THEN start with the other methods.
Until I do hear that problems are starting, I will keep on keeping on, because it is simple, and effective. I am usually BUSY enough, that complicated and time consuming methods go out the window fast. When you add in that those methods, using Liquid OA, or insecticides ACTUALLY harm the bees, and have side effects? Why? JUST, my .02