Charts could show you a period. What they couldn't do was answer the question you had about it, which is nearly always how much, over how long. You ended up reading two points off the axis and doing the subtraction in your head.
Press and drag across a chart instead. The stretch you cover shades in, and a pill tells you what the line did across it: the change in money and in percent, the two dates, and how long it ran. It follows your cursor while you drag and stays put when you let go. Escape clears it, or the ✕ on the pill. Panning is Shift and drag now, because a plain drag had to mean one thing or the other.
Under the chart there's a navigator, a strip of the whole history with your visible window drawn on it. Drag it to move through time, or grab an edge to widen or narrow what you're looking at. The series is sketched in behind the track, so you can see where you're heading instead of guessing at dates.
Both of those are on the stock price chart and on your portfolio's performance chart. While we were in there, the period buttons above them became one segmented control, and they stopped claiming a period is still selected after you've zoomed or dragged away from it.
