Please expliain this formula for me..thanks alot!

[pedie]

Some days back i ask a question on percentage increase & decrease trend calculations....and i think i got something i needed...
however i need to know how it works: link is below.

formula;
=IF(B1="","",(B2-B1)/B1)

Please tell me why we put =if(b1="",""? instead of directly inputing
=(B2-B1)/B1)???
http://www.mrexcel.com/forum/showthread.php?t=478659

Thanks in advance. Please help...

 

[Special-K99]

IF B1 is blank the result is blank, ie you cant perform a calculation on two numbers if one of the numbers does not exist.

In this case B1 would be zero
anything divided by zero is infitnity and would produce a #DIV/0 error

 

[baitmaster]

it returns a null string rather than an error, which you will get for values of "" in B1. It still doesn't pick up div/0 errors for values of zero in B1, so this should also be included

maybe

=IF(OR(B1="",B1=0),"",(B2-B1)/B1)

to prevent this error