public final BigDecimal getContributionMargin() {
BigDecimal ownProductionCostCustomer = getCost("Egenproduksjon",
"Kunde");
if (ownProductionCostCustomer != null
&& ownProductionCostCustomer.intValue() != 0) {
BigDecimal ownProductionCostInternal = getCost("Egenproduksjon",
"Intern");
if (ownProductionCostInternal != null) {
return ownProductionCostCustomer
.subtract(ownProductionCostInternal);