Adjusting fan belt tension?

Just replaced the fan belt driving my AC compressor. It's not a serpentine belt. It only drives the AC Compressor. I'm just curious what others use as a guide for tightness on the belt. I have a couple that I use, one being at the midpoint between the two pulleys the belt should be able to roll by hand 90 degress and no more, the other is about a 1/2 inch play at the midpoint. What do you use?
Thanks
Brian