Displaying Price Data

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You may ask ChartOverlay to display in the title bar the price corresponding to the cursor position. This requires that you provide ChartOverlay with hints, which you can do by right-clicking on any chart point in the overlay window. After clicking, choose Set Price Here from the menu and the Set Price dialog will appear. Enter the price corresponding to the point you clicked; then do it again for a second price.

Once you have set two prices, ChartOverlay will display prices like this:



This feature has an important limitation. Your computer screen is divided into a fixed number of pixels, each of which occupies a small (but non-zero) amount of space. This differs from a mathematical point, which has zero size.

Suppose you are viewing a chart in which prices range from $10 to $30 and suppose the price area of your chart is 5 inches high. Suppose also that your computer screen can display 100 pixels per inch. That would mean that your chart would have 500 (5 x 100) pixels in which to display 2000 cents ($20), or one pixel for each 4 cents of range. Thus, when ChartOverlay reads your cursor's location from the screen, it can only determine price to within a 4 cent range, that is to within ±2 cents; it doesn't know which of four possible values is correct.

Because of this, when ChartOverlay displays a price, it also displays (± error) to remind you that each pixel in your chart is normally associated with a range of prices due to the scaling done by your charting program.