一個例子：客戶在銷售訂單行項目上建立了一個擴充字段A，這個字段的值是最終使用者手動輸入的：
An example: Suppose customer has already created one extension field named “Special Net Price” on Sales Order item level.
然後客戶又建立了另一個擴充字段B：
Now customer would like to see one more extension field “Special Total Value” whose content is calculated as :
Special Total Value = Quantity * Special Net Price, in the example above = 45 * 100 = 4500 USD.
這個擴充字段B的值是計算而來的，公式是标準字段quantity乘以擴充字段A。
如何實作？
Just create a new Calculated Field in key user tool:
Output: