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The Scada rsg4 zapper looks way more sturdy made than the parazapper i have.
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zappers seems ineffective (or poorly effective) to kill big parasitic worms in a human body, so i don't recommend one.
But if you want to try a zapper, the Scada rsg4 zapper functionalities look very basic for the price.
You want at least a 1000Hz frequency and a 2000Hz frequency (because of the possible effects of harmonics), 30000Hz seems too high and poorly effective (if we assume that the frequencies bandwiths of parasitic helminths measured by Hulda Clark are correct), and you also want a sharp square wave (because it sounds looks lethal), and maybe a higher voltage which can be set. (the constant current functionality of parazapper is a good idea if the constant current amount can be set)