The Mysterious Meter is a scale used in Catherine and Catherine: Full Body which is affected over the duration of the story depending on the choices the player makes as Vincent. The meter affects Vincent's own internal thoughts and ideas during key points in the game and the game's own endings.
While the meter is shown throughout the game, what each side of the meter truly represents is not revealed until the very end of the game when Trisha discusses what the player truly desires. The meter is to said to measure Freedom (Red) and Order (Blue), rather than what one may initially assume is a simple Good and Evil scale.
As a result of the neutral endings of the game being commonly called the 'Freedom' endings, a common solution for players to avoid confusion is to swap the terms "Freedom" and "Order" with "Chaos" and "Law" respectively in reference to another game series made by Atlus with a similar scale, Shin Megami Tensei.
Catherine: Full Body
The mysterious meter acts the same as the original regarding most questions the player is asked within Full Body. However, during certain confessionals in the nightmare stages, the player is asked questions which when answered in a specific way can break the meter. If the meter is broken enough times then the Rin path becomes available for the player from day 6 at the Stray Sheep onwards.