Are they actually effective, or are there multiple "blind spots"? I should go visit someday, just to see it. (Not! I've seen those enough in Hawaii...)
If at first you don't succeed, destroy all evidence indicating that you tried.
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If at first you fail at executing a terrible idea, do it again.
It varies with voltage, because of the terminal strip, which adjusts the voltage. So a Thunderbolt with a 10,000 RPM chopper would be set on a very high tap.