Hi,
Let me use elements from both answers;
"MARA was just an example...one can use the MARA because both have same data element"
"is not going to impact anyway"
What I'm saying is, it does impact, it is important which UOM field a quantity field references, maybe not if you only care about activating the table, but certainly if you care about how the data that gets added to the table is used.
If you are processing data from a quantity field you will need to display that value based on its UOM, as the attributes of the UOM will dictate the number of decimal places displayed. If you are totalling quantities you will need to know that you are only adding values expressed in the same unit (it would make no sense to add 15 kg to 5 cm). There's a reason adding this reference field is mandatory, it's because a quantity field without a unit is meaningless. Adding a reference field from an unrelated table is equally meaningless.
The correct answer is in fact from Raymond "refer to unit VOLEH in table VBAP or copy also this field from VBAP to your append structure".
Regards,
Nick