What this is
Unit is “we keep stock in”: pcs, g, kg, ml, L.
Step-by-step
Open Products → Unit and add units you actually count. On the product, set We keep stock in.
Good to know
aPOS converts 1 kg = 1000 g and 1 L = 1000 ml. Do not create a unit named “Case”. Cases are purchase packs on the product (1 case = 24 pcs).