The grading scale underlying NGC and PCGS is approved by the international numismatic society. The following chart shows the valuation level in number and designation:
Abbreviation Numerical Value Designation
MS 60-70 Mint State (Uncirculated)
german: Stempelglanz (st)
AU 50, 53, 55, 58 About Uncirculated
german: Vorzüglich bis Stempelglanz (vz-st)
XF 40, 45 Extremely Fine
german: Vorzüglich (vz)
VF 20, 25, 30, 35 Very Fine
german: Sehr schön (ss)
Issues of mintages in proof-quality (german: Polierte Platte (PP)) are also graded referring to these valuation levels. Proof coins also feature all levels from 1 to 70 in connection with the abbreviation PF or PR. However, sometimes, rather seldom thoug, you will find coins which appear with the traits of a proof-coin and, thus, indicate a somewhat special conditioning. Still, these coins are no real proof. That why they feature the supplement PL, proof like or SP for specimen.
The highest possible grade is 70. However, this grade is absolutely rare. NGC, for instance, is only grading coins with the valuation level MS or Proof 70, if the coin does not show any impairment even at a fivefold zoom.