Creating automatically extended plot ranges

To force Excel to update your chart automatically when you add new data, follow these steps:

   1.   Create a worksheet.

   2.   Select Insert -> Name -> Define to bring up the Define Name dialog box. In the Names in Workbook field, enter Date. In the Refers To field, enter this formula:

= OFFSET (Sheet1!$A$2, 0, 0, COUNTA (Sheet1!$A:$A) - 1)

   3.   Click Add. Notice that the OFFSET function refers to the first data point (cell A2) and uses the COUNTA function to get the number of data points in the column.

Because column A has a heading in row 1, the formula subtracts 1 from the number.

   4.   Type Sales in the Names in Workbook field, and in the Refers To field enter

= OFFSET (Sheet1!$B$2, 0, 0, COUNTA (Sheet1!$B:$B) - 1)

   5.   Click Add and then click OK to close the dialog box.

   6.   Activate the chart and select the data series. In this example:

• X Values: Sheet1!$A$2:$A$15
• Y Values: Sheet1!$B$2:$B$15

   7.   Replace the range references with the names that you defined in Steps 2 and 4:

• X Values: Sheet1!Date
• Y Values: Sheet1!Sales

After you perform these steps, when you add data to columns A and B, the chart updates automatically to show the new data. To use this technique for your own data, make sure that the first argument for the OFFSET function refers to the first data point, and that the argument for COUNTA refers to the entire column of data. Also, if the columns used for the data contain any other entries, COUNTA will return an incorrect value.