Only half the IF/ELSE statement is working

[Nat6]

Hello, 

I'm trying to say that if the value in the length field is greater than zero then show it, if not then show depth instead. 

Have the following code but its only displaying the length value i.e. "Length: 60cm"

The depth displays as follows: "Depth: cm" so is missing the value

Any ideas what I'm missing here as it works just fine for length, width, height and weight!

Thank you