Help with creating and expression for deducting a certain number from an offset to reference level?

[riikkako]

Hi!

I am completely new to expressions, so this is perhaps a stupid question (and I don't even know is it possible).

But here's what I would want: an expression to get an autotext value that deducts a numerical value (in this care 250 mm) from the attribute "offset to reference level"

As in:

Offset to reference level - 250 [mm]

I am just totally failing to do this. No matter how I try it, it gives me an error message saying the Result Conflicts with Data Type.

Is what I want possible? Running AC24, if that matters.

[riikkako]

Aha!

I actually figured it out myself. The issue was that I was trying to create the expression in a Teamwork project, and thus (why this is a feature in AC, I don't know) I was not able to choose the attribute type "Length".

I created the expression in a separate detached Archicad project and imported it to the Teamwork project, works fine.