There are two ratings used throughout the site:

Absolute

This is a rating against all other competitors regardless of price, availability or time — to know where the item sits amongst what is possible. This should not change over time.

1 - Very poor
5 - Average
10 - The very best

Relative

This is a rating of what is currently, locally or price-comparably available. Any number of factors can go into this list of restrictions and it may change over time.