Both actually, unless you set the richteroverride, in which case it isn't random. The 'richterscale' is set to escalate a little less intensely than the real Richter Scale, the script's is set:
Code:
richterscale = [1, 3, 6, 9, 12, 15, 18, 21, 24, 27],
The magnitude is the index of the scale + 1. In some browsers it is harder to differentiate visually between the various magnitudes than it is in others though.
All of this (as regards the scale and magnitude) was already worked out in the original script.
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