Use of several instruments for one transaction

(1) Unless otherwise provided, where several instruments are executed for effecting a transaction chargeable with one ad valorem duty, the principal instrument only shall be charged with the advalorem duty, and every other instrument shall be charged with such other duty as it may be liable to, but the last- mentioned duty shall not exceed the ad valorem duty charged on the principal instrument. (2) In such a case the parties may determine for themselves which instrument is to be stamped as the principal instrument. 20 [CAP. 64