Level 1, Ambient Residue. Faint, emotional in character, non-specific, unreliable for content. Found in corridors, old transport vehicles, hotel rooms used by many people for many years. Often not personal, you are accessing a general accumulated quality of the space, not a specific event. I treat Level 1 as background noise and generally do not log it unless it is unusually strong or unusually specific.
Distinguishing feature: emotional, not informational. You feel something without being able to say what. Usually not worth stopping for unless the quality is distinctive.
Level 2, Structural Presence. Something from your own past, accessible as presence rather than memory. You are not remembering, the event is there, with you, in the space. Quality is specific: you can usually identify whose past it is and roughly when. I have learned to receive Level 2 without collapsing into it. It helps to hold something.
Distinguishing feature: personal recognition. You know this because it is yours. The access is specific enough to be described.
Level 3, Historical Presence. Something from before you, in the space. The key distinction from Level 2: you do not recognize it personally. The access has density but no familiarity. Level 3 presences tend to be old and tend to have accumulated through repetition rather than single events. A space where the same kind of thing happened many times carries more Level 3 weight than a space where one important thing happened once.
Distinguishing feature: density without personal recognition. Strange and specific simultaneously. Touch helps with Level 3 in ways it does not help with Level 1 or 2.