Proof spirit

For excise purposes the strenth of alcohol is calculated in terms of proof strenth.in USA 50%(BY VOlume)alcohol is considered to be 100 proof.IN INDIA 57.1 volumes of alcohol is considered to be equal 100 volume of proof spirit. Any strenth above PS is expressed as over proof(o/p) and any strenth below PS expressed as Under proof(u/p).....,PS=proof spirit....thanx