Each bar shows open (left tick), high–low range (vertical line), and close (right tick). Walnut = bullish session. Blood-red = bearish. Dashed line = 10-session SMA. Hover for detail.
An OHLC chart encodes four price dimensions per time period with a single symbol. A vertical line spans the session's high and low — the full intraday range. Two horizontal ticks branch off this line: one on the left at the opening price, one on the right at the closing price. The viewer reads the symbol's length as volatility (tall = high-volatility session), the tick positions as the session's net direction (close tick above open = the market gained), and the color as a single binary judgment (bullish or bearish).
The perceptual contract is position along a common scale — the y-axis — applied to four values simultaneously through a single glyph. No other chart type encodes the full OHLC tuple per period in comparably compact form at high session counts. At 41 sessions, each OHLC bar takes about 14px of horizontal space. A grouped bar chart rendering the same four values per day would be unusable.
The candlestick chart encodes the same four values but uses a filled rectangle (the "body") for the open-to-close range, with thin wicks extending to the high and low. The body's fill distinguishes bullish from bearish. For sparse time series (weekly, monthly data, or fewer than ~20 sessions), candlestick bodies are immediately legible. For dense series — 40+ daily sessions — the filled bodies begin to occlude each other, and the chart reads as a mass of colored blocks rather than distinct symbols.
The OHLC format uses only lines. At 41 sessions in ~820px, the tick marks are roughly 6px wide and the stroke is 1.7px — enough to read individually without collision. At the same density with candlestick bodies, body widths would be 8–10px, and adjacent bullish/bearish bodies would visually merge. OHLC was chosen because the session count sits in the density range where tick-mark symbols outperform filled rectangles.
Redundant encoding compensates for the thinner visual weight: the close tick's vertical position relative to the open tick encodes direction without color. A bullish session always has the close tick above the open tick; a bearish session always has it below. A viewer who cannot distinguish the walnut (bullish) from blood-red (bearish) can still read the chart correctly through tick position alone.
A line chart of closing prices would show the January peak and trough clearly, but would erase all intraday information. The session of Jan 18 — in which the price opened at 608.6 and fell 16 cents to close at 599.4, with an intraday low of 596.8 — is analytically significant for food security analysis. The low of 596.8 means that at some point during that session, wheat was accessible at a price not seen since mid-December. A line chart at the closing price of 599.4 would miss this. The high-low range is not noise; it is information about the market's indecision, its volatility, and its potential support and resistance levels.
Unlike bar charts, the OHLC y-axis does not start at zero. For bar charts, a zero baseline is mandatory because bar length encodes absolute magnitude — a bar twice as long should represent twice the value, which only holds when the baseline is zero. The OHLC chart encodes change, not absolute magnitude. The viewer's question is "how much did the price move?" not "how large is the price?" A wheat price of zero has no meaning — the commodity would not exist. Starting the y-axis at the lowest low (approximately 578) and ending at the highest high (approximately 642) maximises the visual resolution of the price movements that constitute the actual data story.
The FT Visual Vocabulary places OHLC charts in the Change Over Time category alongside line charts and area charts, with an additional Ranges quality for the high-low dimension. Its guidance on axis truncation for time-series charts: truncation is acceptable when the analyst's goal is to show change rather than absolute quantity. The OHLC chart's entire purpose is change — this is the one chart type where a zero baseline would be actively misleading.
Financial charts conventionally use green for bullish and red for bearish. The hai palette has no green — the palette was designed for earthy gravitas, not traffic-light signaling. Walnut (p2, #5C3317) is used for bullish sessions and blood-red (p3, #B52C2C) for bearish. The positive/negative distinction is preserved: walnut is darker, warmer, and associated with stability; blood-red is a clear danger signal. More importantly, the redundant positional encoding (close tick above/below open tick) means the color choice does not compromise readability. On black-and-white output, the chart remains fully interpretable through tick position alone — which is the WCAG-correct design.