A fixed asset has a positive acquisition value in the beginning of service life and it's depreciated with some negative amounts. During the service life of this fixed asset, there is a donation or the fixed asset will be sold that (adjustment) puts the net book value to a negative amount. After that positive depreciation's should be able to post automatically, when Parameter "Allow positive depreciation" is activated. Now the parameter is locked after very first deprecation so new design is needed in order to take account this kind of business event.