I want to get a shoe mount flash unit for my 1977 Minolta SRT200. My question is about the various numbers I'm seeing on units, for instance, 28 auto, 80px, 128 auto, 132 auto px, and the numbers go to 360px, what do these mean? These are used and near new units that cost about $6-50 on a used equipment site. I'm not a pro, I'm just having fun with an old camera and need a flash unit to take some indoor or low light photos. Thanks.