VINAY,
There are two things to reply.
1. On your specific requirement:
This can not be done because you can not often do it especially in an internal screen of a standard program like the present one.
2. On the requirement of your Customer
I myself am an end-user. End user will have several such requirements that is natural, but they need to be made aware that such things are not possible in standard transactions especially internal screens. Before that a Functional consultant also needs to be aware of how much customization is possible through enhancements in standard screens and where.
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In case the customer presses for such requirements, then it is a big one in development which can be conceived like:
Giving a screen to Customer to create an Order with all the Header details to be filled up in one block. Another block of the same will have operation details. and another will have Components like screen where you can have the Cost field and/or Total cost field also which will automatically be filled upon entry of component and Qty .
And a CREATE button, which creates an Order. (I need not specially mention that the created Order will be like the standard one)
OR
First create an Order with standard transaction, then have a simpler screen described above with only Order number, Operation number and Component details and Cost fields. And then an UPDATE button.
I'm sure you will not be going for a development. This is just to make you aware of how the things usually are here.
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Wish you get better ideas from the forum.
KJogeswaraRao