Setting the Show Value Fields

The Show Value list determines the values that are plotted on the chart. On a standard vertical chart, this is where an element is plotted along the Y-axis. For example, in a bar chart it determines how high a bar is drawn on a bar chart. For each field listed, another element is drawn on the chart at each interval. If there is a line chart with three fields, then each field would have a separate line plotting its values.

The Show Value fields are charted using either their actual value or using a summary function. This is determined by what is selected in the On Change Of list. If this option is set to For Each Record, then each record gets charted according to its actual value and no summary calculation is performed. If the option selected is On Change Of or For All Records, then a summary calculation is performed to determine what value to plot. The On Change Of setting calculates a summary value for each group. The For All Records setting plots a single summary value for the entire report. This has the effect of plotting one element for each field listed.

The default summary calculation is the Sum() function. If you had selected a text field for the Show Value field, then the summary function would be Count(). You can change this by selecting the field and clicking on the Set Summary Operation button. This brings up the standard Change Summary dialog box where you click on the dropdown box to select a different summary function.

Meeting the Minimum Field Requirements

The Evaluate setting and Show Value setting work together to determine the X, Y and Z axis on each chart. Due to the fact that each type of chart can be unique in how it uses the fields in these settings to create the chart, it is important to know how many fields to put in each setting.

Charts have different requirements for the number of data values it needs to plot each point. For example, a line chart needs two values. The first value marks the time interval and the second value marks where on the chart the point will appear. A slightly more complicated chart, the X-Y Scatter chart, has different requirements. It needs a single value to set the intervals along the X-axis of the chart and it needs two values to mark where the point should appear on the chart. Table 12-5 shows the minimum number of fields required by each chart type.

Table 12-5. Required minimum number of fields for each type of chart.

The middle column, # of On Change Of fields, tells you how many fields are required when you have selected the On Change Of option in the drop-down box. This doesn’t apply if you selected either For Each Record or For All Records. This is because these selections automatically set the interval along the X-axis and you aren’t allowed to add new fields. However, if a chart type has a requirement of two fields, then you won’t be able to use the For Each Record or For All Records options.

The last column, # of Show Values, tells you how many fields are required in the Show Values list. Each chart type requires at least one field and some charts allow you to add an unlimited number of fields. The only restriction is that it is limited to how many can reasonably fit on the chart.