Hello Pravin,
You can use auxiliary key figures for forecasting techniques and also in macros. In fact, they are frequently used to show values that are calculated making use of macros.
Here are the steps to create a auxiliary key figure:
1.Run the transaction /SAPAPO/SDP8B.
2.Switch to change mode and head to the "key figures attributes" tab.
3.Define a new name for your key figure on the field "key figure", and press enter. At the same page you set other fields such as UoM (on the "Attributes" section).
If you plan to use it exclusively for macros, do the above in the macro workbench.
You can check the following link to read more about Planning Book Maintenance:
http://help.sap.com/saphelp_ewm70/helpdata/en/22/58ae39ef1bc751e10000000a114084/frameset.htm
I hope this helps you with your query.
Thanks a lot,
Pablo