http://www.perlmonks.org?node_id=1000513


in reply to Re: Earthquakes in three dimensions
in thread Earthquakes in three dimensions

Untested advice: try changing 
"splot '-' using 4:3:5\n"

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to 
"splot '-' using 4:3:5:1 with points pointsize variable\n"

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or 
"splot '-' using 4:3:5:(2*$1) with points pointsize variable\n"

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In Section Cool Uses for Perl