I expect the heaviest unit I have on wheels is the IBM 709 CPU, in addition to its size and steel frame the whole back end is covered with filament transformers to light the tubes. I can roll it around on a level concrete floor OK, but its a good idea to avoid the cracks or at least roll it crooked (so only one wheel sees a crack at a time, and not straight on) and keep the speed up. But there are other contenders - the 709 power supply units, the motor-generator set for the 7094, the 407 accounting machine, etc. I don't know what any of these weigh off hand and don't have the installation manuals handy. There exist larger units (e.g. old CDC mainframes even apart are in large, very tall pieces; the assembled 709 memory is a T about 4 times the floor space of the CPU) but they tend not to have casters. I wonder what a more recent water-cooled machine (e.g. 3090) weighs, the TCU's (thermal conduction units) can't be very light. On other subjects - a common source of serious mildew smell is the absolute filter in a disk drive. I would check that first. - I'm reasonably certain you can still get blank punch cards. The last bunch I bought maybe 10 years ago cost $75 for 10,000. I've been meaning to get some more now that the collection has a dry home and will try to remember to post info. Paul http://www.teleport.com/~prp/collect/