You open a chart of Harbor Coffee, a fictional company that sells packaged coffee and runs coffee shops, and see a fall from $66 to $33. Another chart of the same days barely moves. Is there a loss to investigate?
Imagine Harbor splits its shares two-for-one next year. Both charts start with the same trades. One keeps the old prices; the other restates them to match the new shares. The apparent cliff disappears.
Before treating the plunge as bad news, check the settings. A chart's shape only makes sense once you know what it measures.
Read the labels before the line
A stock chart arranges selected historical prices through time. Technical analysis studies patterns in price and trading activity. This optional track helps you read charts you encounter; a fund-based plan with regular contributions does not need a signal from a chart.
Start at the top: company, ticker, currency and timestamp. Our main chart shows Harbor Coffee, ticker HRBC, in US dollars. For this separate example, suppose Harbor has five future trading sessions at the prices shown. Later lessons reuse these five closes for different tasks; other price paths are separate exercises.
Time runs across the horizontal axis. Price runs up the vertical axis. The chart time span is how much history you see.
The bar interval is how much time each observation summarizes. A one-year chart can contain daily bars or weekly bars. Same span, different detail. Here, the span is five sessions and each bar covers one day.
Check the session label, too. These examples use the regular US session, with dates in New York time. Including extended-hours trading would mean including a different set of trades.
The main chart ends at Day 5's completed close. On a live chart, the last bar can still be changing. Its latest price is only a final close once the interval ends.
Choose what each point contains
A closing-price line chart keeps one close per interval and joins those points. Harbor's five closes are $62, $63, $65, $64 and $66. The line connects those observations; the price may have taken a much rougher route between them.
Candles retain four prices for each interval: the open, high, low and close, shortened to OHLC. The chart overlays a closing-price line on candles so you can see what the line leaves out.
On Day 5, Harbor opens at $64, trades as high as $68 and as low as $63, then closes at $66. The line ends at $66 and hides the visit to $68. The candlestick lesson explains how to find those four prices on each bar.
The volume pane underneath counts shares traded during each matching interval. Its units here are millions: 0.8 means 800,000 shares, and the final bar represents 3 million. Those are shares changing hands, not a count of different shareholders.
Price and volume share a time axis but use different units. Match daily prices to daily volume, and weekly prices to weekly totals. The volume lesson explains how to judge whether the activity is unusual.
If these five sessions form one week, its weekly closing point is $66. The dip from $65 to $64 disappears from that view. A smoother chart can simply be a less detailed chart.
Check what equal height means
The vertical axis supplies the chart's ruler. A linear price scale gives equal height to equal dollar moves. A logarithmic price scale, often labeled “log,” gives equal height to equal percentage moves.
For a separate illustration, start at Harbor's $66 year-end price and double it twice: $66, $132, $264. Both views place these same prices at three equally spaced month-ends.
On the linear view, the first rise adds $66. The second adds $132, so it occupies twice the vertical distance.
On the log view, each rise is a 100% increase, so each gets the same height. The axis still shows dollars; the spacing does the work.
The ruler changed; Harbor did not. Linear makes dollar gains easy to compare. Log makes percentage gains easy to compare, even when the starting prices differ.
Changing the window can also change the line's angle by squeezing more time into the same width. Before calling a rise “steeper,” compare the dates and scale.
Check what the prices include
In the split example from the opening, Harbor closes at $64, $66, $33 and $34. The two-for-one split happens between the second and third sessions.
To make the earlier prices comparable, divide them by two: $64 becomes $32, and $66 becomes $33. The later prices stay unchanged.
| Session | Raw close | Split-adjusted |
|---|---|---|
| 1 | $64 | $32 |
| 2 | $66 | $33 |
| 3 · after split | $33 | $33 |
| 4 | $34 | $34 |
The raw series drops 50% at the split. The adjusted series stays at $33. The split itself does not halve your investment's value.
The chart adjustment basis tells you how the service restates past data. Some also adjust for cash dividends and other distributions, reflecting the price change when a stock goes ex-dividend. An adjusted value can differ from the price at which a share actually traded.
Labels vary. StockCharts' adjustment guide says even its “unadjusted” daily charts correct for splits; they exclude dividend and distribution adjustments. On another service, check which events the setting covers before comparing the lines.
All four candle prices need the same adjustment basis. Pairing a split-adjusted close with an unadjusted open can manufacture a move that never happened. Some providers adjust historical volume for splits, too.
An “adjusted close” label alone does not tell you whether dividends are reinvested. Even a chart that includes reinvestment does not know when you bought or sold. Measuring returns explains how that affects what you earned.
Read identity and date first, then the settings, then the shape:
| Setting | What to check |
|---|---|
| Interval and span | Time per bar; history displayed |
| Session and timestamp | Regular or extended; time zone; bar complete? |
| Axis scale | Equal dollars or equal percentages |
| Adjustment basis | Splits only, distributions too, or raw |
For Harbor, the split explains the $66-to-$33 cliff. It is not evidence of a 50% investment loss. The main chart reads: daily, regular US session, linear, unadjusted, through Day 5's close in New York time. With the settings settled, you can read the body and wicks of one candle.
In short
- A chart's labels decide what its shape means.
- The same time span can hide different levels of detail: check the bar interval.
- A closing line leaves out the interval's highs and lows; candles keep them.
- Equal height means equal dollar moves on a linear scale and equal percentage moves on a log scale.
- Check adjustments before calling a jump a gain or loss, and match volume to the price interval.