The gain is the ratio of a change in the output to the change in the input that caused the output change. It can go from 0 to as high as you want (if you make it too high, the process will oscillate). Gains are very often between .5 and 3, but can be almost any number.
Reset rate is the repeats/minute. (the tutorial on the site will provide a better explaination). The code on the site is designed to be executed every second, or 60 times per minute. I don't think the reset rate should be above about 30 or it will not respond well. You can execute the code twice per second and change the constants that are now 60 to 120, and increase the maximum reset rate to 60. But I don't think it ever needs to be above 30. The reset rate can be as low as zero.
The derivative is in minutes, is typically less than 2, but can be anything from 0 to about 30.