A data comparison system is described. The system may include a memory, an interface, and a processor. The memory may store a compare data structure containing multiple data item pairs, each pair including a legacy data item of a legacy dataset and a corresponding new data item of a new dataset, and a tolerance associated with each data item pair. The processor may receive the compare data structure and the associated tolerances. The processor may call a compare data subroutine to compare each data item pair in accordance with the associated tolerance if the data items are fields. Otherwise, the processor may recursively call the compare data subroutine for each record the data items until the data item are fields. The processor may then compare data items in accordance with the associated tolerance.