Get cell value as #NA - Excel Function NA()

You must be wondering that every time I try my best to avoid #NA in excel sheet but why is this post talking about getting #NA as output. Well #NA is very important at many instances and very useful in charts. We will discuss that later. 

Function to get #NA is
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NA( )
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I.e.
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If(B1=0,NA())
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Then whenever value of B1 cell is Zero then output of formula will be #NA