By Cory Janssen, Chad Langager and Casey Murphy
In technical analysis, charts are similar to the charts that you see in any business setting. A chart is simply a graphical representation of a series of prices over a set time frame. For example, a chart may show a stock's price movement over a one-year period, where each point on the graph represents the closing price for each day the stock is traded:
Figure 1 provides an example of a basic chart. It is a representation of the price movements of a stock over a 1.5 year period. The bottom of the graph, running horizontally (x-axis), is the date or time scale. On the right hand side, running vertically (y-axis), the price of the security is shown. By looking at the graph we see that in October 2004 (Point 1), the price of this stock was around $245, whereas in June 2005 (Point 2), the stock's price is around $265. This tells us that the stock has risen between October 2004 and June 2005.
There are several things that you should be aware of when looking at a chart, as these factors can affect the information that is provided. They include the time scale, the price scale and the price point properties used.
The Time Scale
The time scale refers to the range of dates at the bottom of the chart, which can vary from decades to seconds. The most frequently used time scales are intraday, daily, weekly, monthly, quarterly and annually. The shorter the time frame, the more detailed the chart. Each data point can represent the closing price of the period or show the open, the high, the low and the close depending on the chart used.
Intraday charts plot price movement within the period of one day. This means that the time scale could be as short as five minutes or could cover the whole trading day from the opening bell to the closing bell.
Daily charts are comprised of a series of price movements in which each price point on the chart is a full day's trading condensed into one point. Again, each point on the graph can be simply the closing price or can entail the open, high, low and close for the stock over the day. These data points are spread out over weekly, monthly and even yearly time scales to monitor both short-term and intermediate trends in price movement.
Weekly, monthly, quarterly and yearly charts are used to analyze longer term trends in the movement of a stock's price. Each data point in these graphs will be a condensed version of what happened over the specified period. So for a weekly chart, each data point will be a representation of the price movement of the week. For example, if you are looking at a chart of weekly data spread over a five-year period and each data point is the closing price for the week, the price that is plotted will be the closing price on the last trading day of the week, which is usually a Friday.
The Price Scale and Price Point Properties
The price scale is on the right-hand side of the chart. It shows a stock's current price and compares it to past data points. This may seem like a simple concept in that the price scale goes from lower prices to higher prices as you move along the scale from the bottom to the top. The problem, however, is in the structure of the scale itself. A scale can either be constructed in a linear (arithmetic) or logarithmic way, and both of these options are available on most charting services.
If a price scale is constructed using a linear scale, the space between each price point (10, 20, 30, 40) is separated by an equal amount. A price move from 10 to 20 on a linear scale is the same distance on the chart as a move from 40 to 50. In other words, the price scale measures moves in absolute terms and does not show the effects of percent change.
If a price scale is in logarithmic terms, then the distance between points will be equal in terms of percent change. A price change from 10 to 20 is a 100% increase in the price while a move from 40 to 50 is only a 25% change, even though they are represented by the same distance on a linear scale. On a logarithmic scale, the distance of the 100% price change from 10 to 20 will not be the same as the 25% change from 40 to 50. In this case, the move from 10 to 20 is represented by a larger space one the chart, while the move from 40 to 50, is represented by a smaller space because, percentage-wise, it indicates a smaller move. In Figure 2, the logarithmic price scale on the right leaves the same amount of space between 10 and 20 as it does between 20 and 40 because these both represent 100% increases.