Can I have mannual condition value as zero in Sales order

Hi

I need to enter a mannual condition type in sales order in %, but it should not give me any value and it should be zero. In Pricing procedure I haven't maintained any values in from & to column, but then it is taking the value either from the base price or from some other value. Can any one tell me how to control this....and get zero as value in sale order though I enter in %.

Regards,

Ragu