Different units in one shop

Hi, I would like to have some articles sold by molume (m³) and some by piece (per stuk). is this possible ?
I tried adding a custom field an making it visible in the backend only (made it a single item dropdown box with values "stuk", "m³" and "m") ... but I could not find how to change the content of this field in the backend. I found somewhere else how to change this in the frontend (the text behind the price) ( www.hikashop.com/en/forum/2-general-talk...ter-price.html#85659 ) but since I can't change the unit of an article in the backend (yet) I haven't even gone there yet.

I keep looking at the product-page and the category-page, but I can't seem to find it.

I'm not sure if i can use the volume fields ... Can I leave some of them empty to make it a lenth article? I want the customer to be able to enter the dimensions he wants.
I'm making a proof of concept for a customer and he wants the user to enter width and length for some articles and piece for others. In the screenshot i attached i used m3 (my proof of concept sells volumes of air) but it should be more dynamic if possible. He sells parts by piece and mounted products by length x width (surface)

That is why i made a custom field and wanted to change it in the backend for every item ... That way every item could have its own unit... I thought

I think I found out more ...

I needed to create the custom field in the PRODUCT table ... not in the item-table... that way it is editable in the backend just fine ... now to replace the PER_UNIT with my own custom field ...

I added

if (isset($this->row->verkoopeenheid)){echo $this->row->verkoopeenheid;}else{echo JText::_('PER_UNIT');}

to the Product/listing_price.php instead of echo JText::_('PER_UNIT'); for my templates frontend and that did the trick ...

I can now choose per product what the sales-unit is and it shows up on the frontend ... nice ... thanks for the help

I LOVE this kind of flexibility ... thanks