The grid is the room at ear height. It pokes up red where bass piles up (boom) and dips blue where it cancels (a null). Drag to spin · scroll to zoom. The grey box is the room's real size.
That needle was the corner pressure spike — at a mode frequency the bass piles up hugely in the corner (which is exactly why bass traps go in corners). The old version scaled everything to that one corner, so it shot off the top. Now the scale is compressed, so you see the real hill-and-valley pattern instead of one spike. Slide onto a mode (use the buttons) to see a clean standing wave; slide high and it goes flat — that's the room behaving.