dx=an infinitesimally small number that is greater than 0, as would be defined for a function f(x). If you subtract dx from 1 you should have a number that is less than 1 but as close as possible. dx approaches 0, but dx never gets there. If dx was 0, you would not be able to calculate the slope of a line, dy/dx. In fact 0.999... should be equal to 1-dx

This guy's running a business. If he's using industrial equipment, he should be in an industry-zoned location. Why would he be running it out of his house? Save money on a building? Avoid paying property taxes? Avoid OSHA regulation? Not so noble. It's not like he's a weekend inventor with contraptions in his basement that likely would only hurt himself. This is heavy-duty equipment (20T) that will be used by a (presumably) for-profit company.