you need to adjust volume too. read how stockcharts do it…
At StockCharts, we adjust our historical price data to remove gaps caused by stock splits, dividends and distributions. That may cause our charts to look different from other services that do not perform the same adjustments.
For example, if a stock splits 2-for-1, the price is suddenly half of what it used to be, creating a large gap down on the chart. If you were unaware of the split, the chart would give you the impression that something bearish happened to the underlying company. In addition, most of the technical indicators on that chart would give sell signals because of the big drop in prices. Even though such a split is generally considered a neutral event, an unadjusted chart would contain lots of bearish signals.
In order to prevent these kinds of misleading signals from appearing on our charts, we adjust all the historical data prior to the event. In the case of a 2-for-1 split, we divide all of the historical prices for the stock by 2, then multiply all of the historical volume by 2 so that the bars prior to the split match up smoothly with the bars that appear after the split.
In addition to performing adjustments that remove large gaps caused by splits, we also adjust our historical data to remove smaller gaps caused by dividends and distributions. By making these additional adjustments, we ensure that all price movements on our charts are caused by pure market forces - that is, the forces that Technical Analysis attempts to identify.
While these adjustments are very important for accurate technical signals, they can cause problems in the following circumstances:
Our adjusted historical price data cannot be used to determine the actual buy or sell price for a stock at some point in the past.
Our adjusted historical price data may not match up with unadjusted data from other sources.
Adjusting historical price data can cause P&F reversal points to change if “Traditional” box scaling is used (the default).
Whenever a stock’s historical data is adjusted, we add it to the list of recent adjustments on our Recent Data Adjustments page.
IMPORTANT NOTE: If you want to see an unadjusted chart for a stock, add an underscore character (“_”) to the front of the ticker symbol.