The marker was drawn from a bucket index while a click reported a fraction of the track. Those are different quantities: bars each occupy one equal slot whatever span of time they cover, and the index snapped to the containing bucket's start edge, so the marker landed at the top of whichever slot held the instant — close enough to pass on a dense uniform axis, plainly wrong on a sparse one, and never under the click. Send the fraction instead, computed as the exact inverse of the interpolation the scrub handler applies, and position the marker from it. Marker and click are now the same quantity by construction. Scrolling the grid also left the marker behind: only an explicit scrub ever wrote the position, so the axis claimed to say "when you are" and stopped being true the moment the wheel moved. Map the first visible row back to a capture time and move the marker with it. That runs on every scroll event rather than behind the window-reload guard, which fires a few times per screenful and would make the marker advance in jerks. Only the marker moves, not the bars: rebuilding those means a GROUP BY aggregate over the library, far too much for a flick, and they do not change as the grid scrolls anyway. Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>