basic theory of the formula of new amount field in the serv. inv. line price adjmt

Dear All,
I would like to ask you about what are the primary reason or basic theory
that new amount in the serv. inv. line price adjmt have the formula :

  1. new amount = amount / sum of the amounts on all lines * value to which to adjust
  2. new unit price = new amount / qty

Is it static formula ? Can I customize accroding to the company policy?
Tku for ur answers beforehand.

Rgds,
Mark

Where is this field?
How to you get to it?
What are you doing?
What are you trying to achieve?