I haven't seen this discussed lately. What guides you in determining if a slow pitch is higher than 12 feet?

Pure judgment. I was brought up using the bill of my cap. I have always worn my cap in a certain manner which places the bill (8-stitch) at just around the 12 foot limit.

Regardless of what an umpire uses whether their cap, a building in the distance, tree or fence lines, once you establish it, stay with it. The pitchers need to know so they can adjust. If you move it around, it will possibly frustrate the pitchers and that could make for a very long game.

Same here, Use the bill of the cap. As soon as I lose sight of the ball, illegal pitch. I don't know if it is actually 12 feet, but it is the same for every pitcher and the same every game.

Many umps say they use the bill of the cap, but I haven't been able to make that work. Same with trees, light towers, etc. I keep thinking that slight shifts in where I'm standing will cause large shifts in what looks high.

I just try to watch for it on every pitch, and if I don't see a soft arc, it's high. I admit that I've often wished for some sort of laser device that buzzes if the pitch breaks the 12-foot plane.

Around here, some umps won't call a pitch high unless it's way up there. Others (like me) keep a tight rein. Naturally, this causes the pitchers to adjust for each game.