They first convert the amps to wattss by multiplying 1.6 x 120 volts. This comes out to 192, yes, different than the 240KwH. But there is a power factor that is also added in by the manufacturer, so that's why the math doesn't seem to work. Here's a link that will explain it all and how they come up with the numbers that they do.
http://www.signs.org/Technical/artic...ItemNumber=624