2.5 Constrain Location Z of one object to Dimension Z of another

I would like to have the location Z property of object A equal the dimension Z of object B. This way when I change the height of B, the location of A matches it. How would I go about doing this? I can’t find a constraint that seems to allow this.

I am using 2.5.4. If you need more details please let me know. Thanks for your help.

Hi, use the Transformation constraint or setup a driver…