Cox Automotive is celebrating the centennial of Kelley Blue Book, the iconic source of vehicle values.

The compilation started literally as a blue book put together by Los Angeles car dealer Les Kelley called the “Blue Book of Motor Car Values.”

It originally was a list of used cars Kelley sought to buy along with the prices he was willing to pay, said Cox, whose Autotrader subsidiary bought the enterprise in December 2010.

The book became a standard reference far beyond its creator’s Kelley Kar Co. as his fellow dealers, along with lenders, started asking for the prices. Kelley based them on the market savvy he’d amassed since opening his dealership in 1918.

He later expanded the book’s metrics to include mileage. As he moved from retail to focus on publishing, his company added its New Car Price Manual in 1966 and its first consumer manual in 1993, putting the data online in the mid-1990s.

Today’s values hinge on a much wider array of factors, including vehicle condition and location, in addition to trade-in value versus private-sale value.

“The original Blue Book offered a common reference in a marketplace where information was unevenly distributed,” Cox Senior Advice Editor Chris Hardesty writes.

“A century later, the tools are faster, the data is more comprehensive, and the calculations are more sophisticated. Yet even the most accurate valuation is a starting point, not a guarantee of what a particular vehicle will sell for.”