Have you tried debugging?
Have you tried to find this variable?
I didn't find this variable, I don't know if this variable exists
Do you know the variable or some other way to get it？
To find variable or to find out the variable exists you have to do debugging.
How do you tried to find variable - any variable? Where were you looking for variables?
(Ive found them in nx11.0.2, I dont know if they exist in nx8.5)
This caused creating of 3 extra files: proc, debug,review
(It also takes more time to postprocessing.)
Open *.debug file.
There is a list of variables.
Try to find value of variable you want to find or try to find some string.
In your case try to fing "length" or lenght value 561.... or 567.... (be careful, values are not rounded).
By this technique you can find out if variable exists and then you can use it.
Ofcourse it has to exist in time when you want to use it in PB.