Read the conditions
A has no opening. B keeps only the current opening. C keeps the current opening and reduces the opacity of lines inside the immediately previous opening to 18% of their usual value. C replaces that trace at each move; it does not accumulate all earlier positions. The trace uses the previous opening's actual omission mask.
All three fields share 121 rows, the same waves, palette, phase and base line opacity. The opening also changes nearby line curvature, as in the original drawing. The initial comparison is already one move away from the original position, so C has a previous location to show.
This is a study following A Place Left Open, not a replacement or a second finished work. Phase changes are manual; there is no automatic animation, sound, tracking or saved visitor state. The faint trace is a choice to compare, not an assertion that remembering is better.