Power Gauge

The Power Gauge is the system developed and used by the Vanguard to categorize characters within Highschool DxD: Blazing Dusk & Midnight Dawn based on their magical power and on rare occasions, physical strength. It is done mostly numerically.

0
Regular humans, animals, and other creatures with absolutely no magical power.

1-99
Anyone from the weakest magic user (including but not limited to Issei when he was initially revived) to just below the average low-class devil. Can also apply to sorcerers who've just started their training.

100-199
The varying power degrees of a normal low-class sorcerer, devil, angel, fallen angel, etc. Examples: Issei (Vol. I-II), Raynare (pre-revival), Kiba Yuuto (Vol. I-II), Koneko Toujou (Vol. I-III), Asia Argento (Vol. I-III), Genshirou Saji (Vol. I-III).

200-299
The stage between low and middle class. Examples: Issei Hyoudou (Vol. III-V), Genshirou Saji (Vol. IV-VI), Koneko Toujou (Vol. IV-V).

300-399
Beings with middle-class magical power. Examples: Issei Hyoudou (Vol. VI), Kiba Yuuto (Vol. III-VI).

400-499
The stage between middle and high class. Examples: Akeno Himejima (Vol. I-V).

500-999
High-class power. The reason it's so broad is that there are numerous characters strong enough for this category that simply aren't good enough for the higher-up categories. Examples: Rias Gremory (Vol. I-?), Akeno Himejima (Vol. VI-?), Issei Hyoudou (Vol. VI-?).

1,000-9,999
The stage between high and ultimate class. Examples: Michael Eon (Vol. I-VI).

10,000-99,999
Ultimate-class. Examples: Zach Praktum (Vol. I-?)

100,000-999,999
The stage between ultimate and Satan/Seraph/Gov. General-like power. Examples: Azazel, Shimezhai, Michael the Archangel, Gabriel, Metatron.

1,000,000-9,999,999
Gods, Super Devils, certain monstrous gods, and the Heavenly Dragons. Examples: Demiurge (AKA God of the Bible), Sirzechs Lucifer, Ajuka Beelzebub, the Leviathan God, Ddraig, Albion, Ddraig's Clone (Formerly).

10,000,000-∞ minus 1
The amount of power reserved for those who are above the normal gods and can easily bring about the end of everything. Known Examples: Ophis, Great Red, Trihexa.

∞
Infinite power. Anyone with this strength is absolutely impossible to overcome except by someone else with this power. Examples: Azrael (Lord of Balance), Satanael (Lord of Order), Kaira (Lady of Chaos).