Abstract: A transaction system of a supplier includes a margin determination unit comprising margin table memory for storing a plurality of tables (such as financial exchange and money market margin tables), each table having rows for the table name, transaction type, client details or rating, transaction size, transaction currency, instrument type, time period(s), and margin type and amount. A selection module sequentially selects tables from memory and a comparison module compares quantities specified by successive rows of the selected table with corresponding quantities in a transaction request from a client/user. A calculation unit calculates a margin based on information in the table if all comparisons are good; otherwise the next table is selected. A table editor allows easy updating of the tables (adding new tables, and deleting, amending or re-arranging existing tables).