Suppose you are planning to implement a change request and want to know how long it will take to complete the change. In that situation, you typically run an effort estimation report for your project based on weighted values for selected complexity metrics.
But what if your own analysis of the project shows that a given program will actually take much less time to change than the weighted calculation would suggest. The program might have thousands of source lines, for example, increasing its calculated complexity, while actually being very easy to modify.
A change magnitude is a way of overriding the calculated value for a source file. Your "subjective" estimate of the effort involved, Small, Medium, Large, Extra Large, becomes an input to the effort calculation, along with the weighted values.
You can specify a change magnitude in the Interactive Analysis Source or Context pane, or in the Effort Estimation tool itself. Select the source file and choose Set Change Magnitude in the right-click menu. Set the change magnitude to S for Small, M for Medium, L for Large, or XL for Extra Large. The effort estimation calculation for the selected file is automatically updated.