Section 29

A security for the payment or repayment of money to be lent, advanced or paid, or which may become due upon an account current either with or without money previously due, is chargeable, where the total amount secured or to be ultimately recoverable is in any way limited, with the same duty as a security for the amount so limited.

Where such total amount is unlimited, the security is to be available for such an amount only as the ad valorem duty impressed on the security or denoted by the stamp certificate attached to the security (as the case may be) extends to cover; but where any advance or loan is made in excess of the amount covered by that duty, the security is for the purpose of stamp duty deemed to be a new and separate instrument bearing the date on the day on which the advance or loan is made.