Solar Flare classification origin

[Rules For]

Does anyone know the origin of the A, B, C, M, X classification system for solar flares? I'm curious as to why it jumps from C to M and then to X (instead of A, B, C, D, E, for example). I figured there might be a historical explanation, like with the OBAFGKM stellar classification system, but searching online I've so far come up empty-handed.

[neufer]

Click to play embedded YouTube video.

Does anyone know the origin of the A, B, C, M, X classification system for solar flares? I'm curious as to why it jumps from C to M and then to X (instead of A, B, C, D, E, for example).

The A, B, C's are mere child's play.

M & X are warnings

The Roman numeral M is 1000 ... times stronger than an A class
The Roman numeral X is 10 ... times stronger than an M class

[Chris Peterson]

Click to play embedded YouTube video.

Does anyone know the origin of the A, B, C, M, X classification system for solar flares? I'm curious as to why it jumps from C to M and then to X (instead of A, B, C, D, E, for example).

The A, B, C's are mere child's play.

M & X are warnings :!:

The Roman numeral M is 1000 ... times stronger than an A class :?:
The Roman numeral X is 10 ... times stronger than an M class :?:

I think that A and B classes came later. The original classification (using peak x-ray flux) was C, M, X. Which, with 100, 1000, 10 doesn't quite fit the Roman numeral hypothesis. Compact, medium, extreme? Common, medium, x-ray? Not sure, and not obvious.