does not necessarily determine exact value. Even within the same grade, coins can have widely differing values. In the May 26, 2003 edition of Coin World, the hobby newspaper had announced they had contracted investigators to conduct a year-long, comparative study of PCGS, ACCGS, and NGC, along with several other grading services, each known as Third Party Grader (TPG). In their investigation, Coin World sent the same coins to each grading service over the course of a year, each coin being graded by all Third Party Graders it was sent to. They found that "In no case did the grading services agree on the grade of any given coin, and in some cases the difference in grading was as much as seven points off". The NGC grading scale is based on the 70-point Sheldon coin grading scale. Strike designations include Prooflike and Deep Prooflike for circulation issue coins and Cameo and Ultra Cameo for Proof coins. Coins deemed high-end for their particular numeric grade receive a "Plus" designation. Coins considered attractive get a "Star" moniker. Cleaned, scratched, or otherwise impaired coins can be encapsulated and assigned a verbal "details" grade, but not a numerical one. Additional information is also given for graded and labelled mules and mint errors, specifying the particular error in addition to a numerical grade. NGC has used EdgeView Holders since 2007 for the Presidential Dollar series and for all other coins since 2008. Since 2009, a scratch-resistant holder coating, similar to that used on eyeglass lenses, has been employed. NGC offers Oversize holders for coins larger than 45 mm and up to 120 mm, and Mega holders for coins larger than 120 mm and up to 180 mm. NGC's label lists a coin's denomination, variety, grade, pedigree, serial number, and other info. Online research tools NGC Cert Lookup verifies all NGC certified coins and helps combat against holder counterfeiting. Using the label serial number, NGC will reveal a coin's date, denomination, grade, photo (if any), and pricing and Census info. NGC Coin Explorer lists key info about many coin issues, such as mintages and values. The NGC Census reports how many examples of each issue NGC has certified by grade, which helps determine relative rarity. Census figures are often falsely inflated due to resubmissions of the same coins. NGC Coin Price Guide lists pricing data for most US coin (and some modern Chinese) issues. NGC Auction