I am building a little spreadsheet that needs to find if an adjacent cell has a value. Then make a calculation using that value or leave blank. It seems like an easy question, but this is my first time using Numbers and the solution escapes me. Here is my formula (the one that does not work)

If(isblank(B2),null,(238-B2)/238)

If B2 is blank then enter a null value, else run the calculation. If B2 is blank, then the current cell should be null or blank.
Any ideas?

I use excell so I'm not too sure about numbers but I think your use of the word "null" is what is tripping you up.

Substitute an empty set of quotes in place of the word "null" and see if it helps.

If(isblank(B2),"",(238-B2)/238)

That did it. Double quotes. Thank you. Numbers is actually pretty powerful, if you just know the tricks.