Understanding a notification phrase

Amit (Accountant) (261 Points)

23 May 2011  

In notification  number 2/2008 and in some other notifications, the phrase "from so much of the duty of excise leviable thereon as ......."  has been used to impose a rate of duty  (14% in the aforesaid notification).

I wonder why they do not simply write 14% adveloram whatever other figure they want to impose instead of using the above phrase?

Any one interested in such trivia?