food scale

I have a little mechanical food scale. I use it. It helps a lot. I'm ready to upgrade. I'm looking for a digital scale, that will allow me to punch in the calories per serving of an item. then weight the item. and tell me how many calories the food is, even if the weight is different than the serving size on the box. does that make sense? Right now I'm using a calculator to find out my foods calorie-per-gram based on the serving size calories on the box; but its tedious. I'd like some fancy scale to tell figure out the calories for me. Ive seen diet scales online but they seem to use product codes that you enter from a booklet. I don't want that. does anyone know what im talking about and knows if they exist. ok thx!