CAP's Black Book Live service is now showing live prices for vehicles as soon as they are identified.
The company made the change due to the inevitability of monthly guides always being behind the curve when prices change.
In one example a three-year-old Ford Focus 1.4 Style, with 50,000 miles, steadily rose in value from mid-July to mid-September with just one brief dip during late August.
In another example a Volkswagen Tiguan 2.0 TDi R Line was revalued four times by Black Book Live editors over the space of five weeks, starting at £14,150 on July 16 and reaching £14,750 on August 23.
CAP’s Mike Hind said: “We have long and frustrating experiences of struggling to accurately reflect a fast-changing market – such as the trade price crash of 2008 and the historic upturn that followed.
"The bottom line is, you can’t serve customers properly in a moving market if you can’t move with it.
“We deadline our monthly Black Book around the 23rd which makes it the most up to date book of its kind.
"But even then, if prices turn immediately after that it’s another five weeks before our customers see more up to date trade prices. At that point the market may still be moving so those prices are also instantly out of date.
“Black Book Live takes us out of that vicious circle so that customers see price changes as they happen – meaning they can react appropriately, armed with the latest information."