Sales Documents & calculations + x / -

Hi guys,

I just want to know how can I make some calculation with documents.

Example: I got these 2 fields in my deal, Deal value and Client tax coef

I want to display in my document :

• Deal value : [Deal value (deal value)] (this one is easy)
• Deal tax coef :  [Deal value (deal value)] x [Deal tax (deal tax)] (don't know how to multiply fields)

Is it possible ?