The Arbitron (now Nielsen) Diary:

Nielsen still uses them in markets 51 and smaller

The diary is still used in markets 51-300 by Arbitron, since the methodology is accredited
and vastly less expensive in markets with lower revenue bases. Here is how the diary looked around 2008:

The diary covers one week of radio listening and there is one given for each member of a household This book explains the diary method as it was implemented in the Pre-PPM era. Click on the cover above to read the whole document in PDF form.
How to fill in a Diary
Participants get precise instructions on how to fill in their diary. They are told to show the time, name of station or other identifier, and location of listening for each day of the week.
One of the seven daily pages.
Note how simple it is for a listener of any age or education to correctly indicate what they listened to throughout the day.
Supervisor area at the Arbitron diary placement call center in Columbia where diary keepers are recruited  Another view of the diary processing center in Columbia. This is the area where hard to credit diary entries are validated by callback. 
The Arbitron building in Columbia, MD. Diary service subscribers can visit and review the diaries for their market.   Here is the "Welcome" message board for the stations visiting on one date. I was representing the HBC stations in San Diego and LA as well as Arso Radio from Puerto Rico. 
Computer set up to review  Los Angeles And one for the Puerto Rico review
Arbitron Reference Guide to Understanding and Using Radio Ratings
Ratings Information from Dr- Ed Cohen
A series of FAQ-like articles
was issued in the mid-2000's
 by Dr. Ed Cohen of Arbitron.

Click on any of them to read
 Dr. Ed's insights into the diary survey world.

There are articles about Proportionality,
Minority Measurement and Wobble.