Skin thickness sum

[Karol Lozinski]

Hi! I've got probably a silly question but... is there a way in ArchiCAD 21 to sum cells in a group? For example as show in attached images. I have a wall composite with its skins listed, and skins thickness. All I want it sum of those values so in a first wall I'd like to see 11 cm, not 693 cm. I agree, small difference but noticible. When I choose the sum1 in scheme settings I get number of walls - still not exacly what I need. It seems that what I'm trying to accomplish is fairly simple, though I'm struggling with it. Please, help.