For those interested in a more comprehensive view of the Dvorak technique, including how all storms are broken down into four categories (I was close before - there's also a curved band pattern), the Australian Bureau of Meteorology has an excellent resource available online:

http://www.bom.gov.au/bmrc/pubs/tcguide/ch2/ch2_3.htm

Specifically, read through section 2.3.2 while keeping their figures 2.4(a,b) and 2.5(a,b) open in a separate window.

It may be more information that you ever wanted to know about the technique, but it gives you a comprehensive view of what an analyst goes through when assigning a subjective T-number. It's worthwhile to note that objective Dvorak analyses go through the same process without the human constraints/enhancements (depending on how you want to view it!).