I have read over all the posts but I feel the need to post my two cents.
A micron gauge is essential for any tech. I went to a scotsman class and a true class on the same day. Both their reps asked for a show of hands of who used a micron gauge. I was amazed to see that only 50 percent of the class raised their hands.
The first tech I ever rode with had a micron gauge. A supco I believe. I never seen him use it. Needless to say the first time I had to borrow his truck on a weekend call I went to use the gauge. It didn't even have batteries in it.
After he quit, I put my tools in the truck and hit the road. I ended up going to one of his previous calls on a walkin cooler. System was very, very low on refrigerant. Only about 5psi in the system. I hit it with nitrogen and the whistling noise was apperent. The leak was in the condensor on the top u joint. He didn't even cut away the surrounding steel. He heat it up and threw what looked to be about two sticks of 15 percent on it. I caught hell cutting the steel away and trying to grind down the solder with a cutoff wheel. I did get the leak fixed and haven't heard from them since.
If he would have used his micron gauge he would have know that the leak wasn't fixed.
Hell, nitrogen would have told him the same thing.