Maryland Worksheet A — Child Support Obligation Primary Physical Custody is a form used by the State of Maryland to calculate the amount of child support a non-custodial parent (obliged) must pay a custodial parent (obliged). The worksheet takes into consideration the obliged's gross income, the number of children involved, and other factors such as the custodial parent's income. There are three types of Maryland Worksheet A — Child Support Obligation Primary Physical Custody: Unallocated, Shared Physical Custody, and Split Physical Custody. Unallocated is used when the obliged has primary physical custody of the child; Shared Physical Custody is used when both parents share physical custody of the child; and Split Physical Custody is used when the obliged has shared physical custody of two or more children.