Re: Dear Roger...

The Ext-120 is one of the medical grade ozonators. Here's the info:

http://www.longevityresources.com/htdocs/ozone-generator-ext120main.html

The medical grade units that I am familiar with are:

Plasmafire (Plasmafire.com)
Longevity
Synergy Systems (ebay)

Plasmafire are generally considered the best and use cold plasma. But they are by far the most expensive as well. Longevity and Synergy Systems use cold corona discharge. Plasmafire and Longevity can be calibrated for ozone output, while Synergy Systems is not calibrated. But Synergy Systems if by far the least expensive. That's kind of a general run-down on the pros and cons of each.