Add source terms in usr_source.f

Hi everyone, I want to add source terms in continuity and momentum equations with TFM approach, and source term have this linear equation according to Patankar’s book.
and review a tutorial Absorption_column_2d/usr_sources.f:99 with this nomenclature:

sourcerhs = SCPA + SCPB
sourcelhs = SCCA + SCCB

My questions are:1. The variable sourcerhs corresponds to Sc and sourcelhs to Sp?
2. These must be multiplied by the differential volume element before, or this is performed in subsequent processes?
3. What is the difference between using scalar_prop.f and usr_sources.f in writing the source term?