Local historian Steve Rogstad - who has frequently joined us over the years to talk about Abraham Lincoln - shifts gears with his most recent book, "The Million Dollar Quartet - and the Challenges of Oral Testimony." The title refers to the remarkable occasion when four now-famous musicians - Elvis Presley, Jerry Lee Lewis, Carl Perkins and Johnny Cash - converged one day at a recording studio in Memphis, Tennessee. It's an occasion around which a huge amount of legend and misinformation has sprung up over the years, and Rogstad has done painstaking research to try and sort out exactly what happened on that day in dearly December 1956.