Rhonda - I don't know if anyone has a "right" or "wrong answer to this unfortunately.
I have had a 100% success rate in curing cancer (with my one only patient haha) using the GB4000 and that was using the main unit only - I was not able to take the SRT-4 with me. I treated using auto codes 538 / 436 / 410 / 359 / 242 / 115 and i also ran the codes for candida albicans - apparently no cancer patient has been found who did not also have candida and it is assumed there is some connection there. I ran the codes for the standard 5 minutes - building to 20 minutes after the thrid treatment and moving to treat every day (I only had ten days before I had to return to Canada).
A friend who now has TWO Gb4000s says he is finding better results running only one or two frequencies at a time. What works is what counts and how the patient is feeling in the course of treatment is paramount. There's a lot of intuition required it seems.