I am currently using an old shipping scale for charging and recovering refrigerant, and I recently saw an ad in a trade mag about the "CC220 Compute-A-Charge" Refrigerant charging/recovery scale. Has anyone used it? How helpful is it to have? Would I benefit from getting one, or should I stick with what I have. It looks like it would be worth getting, but I wanted to get an opinion from someone who has used, or is using it, before I spend the money.