As you watch a usability test, you should make minute-by-minute observations of the participant's behaviours as single letter codes: an approach known as datalogging.
Interesting posts about this link
iatvJan JursaInfluentialGood article: "Log usability tests like a pro" by David Travis, http://bit.ly/c3p7ax (userfocus.co.uk)
userfocusDavid TravisInfluentialLog usability tests like a pro. Includes a macro-free Excel spreadsheet to timestamp observations. #uxhttp://bit.ly/a9mBJu