[counter-hijack]
In 1E, it was a straight 1d6 per 10 feet, up to 20d6 at 200 feet. However, IIRC Gary has maintained in Dragon and elsewhere his original intention was 1d6 per 10 feet cumulative, i.e., 1d6 for the first 10 feet, 2d6 for the second 10 feet, 3d6 for the third 10 feet, and so on...