Digital BW, The Print

Elementary question, I suppose! I've been using the MIS refillable carts for my R1800 and resetting them with a chip resetter each time I fill them up. The carts are labeled ARC-TO541-EC, ARC-TO542-EC, etc up through ARC-TO549-EC. If ARC means auto reset, why I am resetting them? Do I need to do that? And what does the EC mean?

I also note MIS sells HT (=Heat Transfer) carts for this printer. Can someone tell me what that means?

Thanks all!