I spent six years collecting statistical data on the effects of zapping, using different methods. The information in the book is the result of that data.
Zapping for less than 7 minutes is not very effective. Microscopic studies show that parasites recover if they are not completely destroyed which takes about 7 minutes.
Zapping for one hour straight does not produce as good of results as 7-20-7-20-7.
The book also tells about how to get much better results.