One way:

B1: =IF(ISNUMBER(A1),A1-<a math calculation,"")

In article ,
Jim wrote:

How do I state IF cell a1 is blank, then b1 +blank also or if cell a1 has any
positive or negative number, including 0, then b1= a1-a math calculation. I
am trying to apply math formulas to multiple columns of test data in which
some cells have no test data.