The industrial scale was a system used to rate the extent of industrial development on different planets.

It is unclear if that there was only one Industrial Scale system that transitioned from letters to numbers or if there were two scales being used though logically the former seems more likely.

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")

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