an "X" rating is a value number stating its worth a certian amount (In this case X).

There is no tie between a value and rarity.

Rarity ratings usually are mentioned in James Campiglias book as an R1-R10 with R10 being the most rare.

Each R# give an estimate of chips known for that rarity.

There are some chips that are valuable but not all that rare and others that are very rare but not all that valuable.

Are you referring to a specific chip? if so I may be able to tell you the R value.

Doug