Interstate sale without form c

Hello friends., can anyone explain me , we are manufacturer of wrist watch dial selling goods outside the state without 'C' @ 12.5 % is it correct.(Haryana to Delhi) And same goods we are selling within state @ 4.20 % against from D1 (HVAT) So please I have a doubt that if we our product are falling under 4% so we should charges 4% while selling the goods outside the sate as full rate of tax. So please help me out.