technical writing - How can I express this more clearly or concisely?

I'm documenting a block of computer code and would like to make it clear and concise. I'm describing a function that populates a field on a user input screen. Here's my best shot but it still seems confusing because the 'in the', 'on the', 'for a' seem like a lot of prepositions for one sentence.

This function returns the WINGNUT_SELLER_CODE that appears in the 'Vendor' field  
on the 'THREADED_NUTS' screen for a given NUT_ID. 

Questions:
[1] How can I rewrite this to make it easier to understand?
[2] What about 'that appears' vs. 'which appears' when should I use 'that' and 'which' ?

Answer

Maybe break it into two sentences?

When you send this function a NUT_ID, it returns a WINGNUT_SELLER_CODE. This code is from the'THREADED_NUTS' screen in the 'Vendor' field.

I almost always use "that". (Every copy editor I've ever encountered seems determined to eradicate all uses of "which".