Changing Order unit in a Contract (ME32k)

Hi,

Can anyone tell me if this is normal that i can not change the Order unit in a contract ? i can change the price unit trough the conditions, but where can i change the order unit ?

For info i enter a material code in the value contract, normal item type.

I think i should be able to change it , because when changing a Purchase info record for the same material/ vendor, i can change the order unit.

Thank you in advance for your quick answers.

Isabelle