Sales Types Effects

Hello,

I noticed that, in the Company Setup, we need to define a sales type for  defining the :

Base for auto price calculations :

Can you clarify that for me plese when it is used inside the Prog and wht it will affect.

Also, in the same circle, can you kindly clarify for me what is the purpose of the :

Tax included :

when defining the a new Sales Type

Regards,

khaled