All the parameters of a reference are displayed in its properties window where you can edit them accurately.
To change the properties
Select the object and perform the following operations:
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					Open the Properties dialog box in one of the following ways: - Double-click on the object. 
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				              Press the key combination ALT+Enter. 
- Click the  button in the toolbar. button in the toolbar.
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				              Activate the context menu with the right mouse button and choose the command Properties. 
 
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					Modify the parameters of the object. To preview the changes, click the Apply button. 
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	              Click on OK.