>- accuracy as in a stable wave form, or the precise frequency number?
There are many specific frequencies that work better for some things and other frequencies that work better for others. In these cases, accuracy is very important.
As for the stable waveform, not sure what you are referring to but there are some who use the term that know nothing about what they are talking. Kind of like the claim of some that they can get even harmonics out of a square wave. Not mathematically possible.
>- As I read from Hulda Clark , she said it doesn't matter what frequency it is, as long as it has a positive offset and is a clean square wave, and it is above 10Hz.
To a certain extent most any frequency can have some effect but no matter what Dr. Clark claimed or anyone else for that matter, there is not any single frequency that gets everything. I proved that with my jar of pond water experiments. While a single frequency may kill some microbes, it is certainly not going to get all.
>- Does the parazapper have a constant voltage or does the 9v drop as the battery dies out?
Depends on the model, but even the ones that do decrease with the battery output have a battery indicator that lets you know when to replace the battery.
If the original Hulda Clark Zapper worked that well, there would never have been a need for advanced products like ParaZapper. There would never have been a need for Rife machines or Lakhovsky MWO's or many others.