Lukas, sorry for the delay in responding. Any variables declared with var are not properties and therefore are not able to be discovered by looping over the object's property names. This kata takes advantage of that, forcing you to look for the variable in different ways. Have you tried to see what the source code looks like?

This is right. The solution description needs to be updated to say that each wall of the box is half a unit thick and that the box is measured from the outside dimensions.