Industrial scale
From Memory Alpha, the free Star Trek reference
The industrial scale was a system used to rate the extent of industrial development on different planets.
There are two scales in use. One is a numbering scheme that goes at least as high as 7, where higher numbers denote a greater degree of industrialization. An example of a Level 7 world is Scalos. (TOS: "Wink of an Eye")
The second industrial scale uses a letter system:
During the mid-23rd century, the planet Sigma Draconis III was a grade "B", and the planet Sigma Draconis IV was a grade "G". (TOS: "Spock's Brain")
