When we post retirement via AS91 or AS92, we could find system has default the field is positive or negative.
Enter revaluation amount 10000. Then enter, the amount will show as -10000.
System will do following check in SAPLALTD， include LALTDI0S:
IF GT_ANTVAL-AUFWV > 0.
GT_ANTVAL-AUFWV = 0 – GT_ANTVAL-AUFWV.
Here we could find if we enter a positive revaluation amount, system will change it to negative.
For other transaction, we could also check the default amount is positive or negative here.