Each currency pair's chart plots exchange rate movement over a period you choose — the shorter windows show more granular swings, the longer ones smooth things out into a trend. Underneath the line, we track the high, low, and closing rate for the period, the same three numbers a trading desk would glance at first.
The gap between the high and the low is the thing most people skip past and shouldn't. A pair that moved between 1.08 and 1.095 over a week is behaving very differently from one that moved between 1.02 and 1.16, even if they both "closed about where they started." The first is calm; the second had a week worth paying attention to, and averaging it into a single closing number hides that entirely.
Closing rate is exactly what it sounds like — where the rate landed at the end of whatever period you're looking at. It's the number people quote in headlines ("the pound closed lower against the dollar today") because it's a single comparable point, but it's the least informative of the three on its own. A currency can close flat after a genuinely wild day.
A few things worth knowing about reading these charts specifically for decisions, not just curiosity:
Trend direction over 30 days tells you more than a single day's move. Currency markets are noisy day-to-day — a pair can swing 0.5% in an afternoon for reasons that have nothing to do with the underlying economies involved. Zoom out before drawing a conclusion from a short window.
Compare the pair against its own recent range, not against round numbers. "USD/JPY is at 150" means nothing on its own. Whether 150 is near the top or bottom of where that pair has traded over the last month tells you whether you're looking at a currency that's currently expensive or cheap relative to its recent self.
If you're timing a transfer or a purchase around a rate, the chart is there to show you context, not to predict where the rate goes next. Nobody's chart does that reliably, including ours. What it's genuinely useful for is telling you whether "the rate right now" is unusually good, unusually bad, or perfectly normal compared to where that pair has actually been trading.