Lets see how the Standard Catalog of World Coins attempts to guide us through grading.
''In grading coins, there are two elements to look for: 1) Overall wear, and 2) loss of design details, such as strands of hair, feathers on eagles, designs on coats of arms, etc. The age, rarity or type of a coin should not be a consideration in grading, Grade each coin by the weaker of the two sides. Grade by the amount of overall wear and loss of design detail evident on each side of the coin. On coins with a moderately small design element, which is prone to early wear, grade by that design alone.
For Brilliant Uncirculated (BU) grades there will be no visible signs of wear or handling, even under 30-power microscope. Full mint luster will be present. Ideally no bag marks will be evident.
For Uncirculated (Unc.) grades there will be no visible signs of wear or handling, even under a 30-power microscope. Bag marks may be present.
For Almost Uncirculated (AU), all detail will be visible. There will be wear only on the highest point of the coin. There will often be half or nore of the original mint luster present.
On the Extremely fine (XF) coin, there will be about 95% of the original detail visible. Or, on a coin with a design with no inner detail to wear down, there will be a very light wear over nearly all the coin. If a small design is used as the grading area, about 90% of the original detail will be visible. This latter rule stems from the logic that a smaller amount of detail needs to be present because a small area is being used to grade the whole coin.
The Very Fine (VF) coin will have about 75% of the original detail visible. Or, on a coin with no inner detail, there will be moderate wear over the entire coin. Corners of letters and numbers may be weak. A small grading area will have about 66% of the original detail.
For Fine (F), there will be about 50% of the original detail visible. Or, on a coin with no inner detail, there will be fairly heavy wear over all the coin. Sides of letters will be weak. A typically uncleaned coin will often appear as dirty of dull. A small grading area will have just under 50% of the original detail.
On the Very Good (VG) coin, there will be about 25% of the original detail visible. There will be heavy wear on all the coin.
The Good (G) coin's design will be clearly outlined but with substantial wear. Some of the larger detail may be visible. The rim may have a few weak spots of wear.
On the About Good (AG) coin, there will be typically be only a silhouette of a large design. The rim will be worn down into the letters if any. ''