I really don't know how to calibrate a scale, sorry and it runs on a lithium battery from the label on the bottom of it. Good questions, ty for asking!
I am not real sure how to answer that, so I will just tell you what was listed on the product page for this item where I bought it from and hopefully it will assist you.
DigiWeigh 250BM
The DigiWeigh scale offers (4) different weighing modes: Grams, Ounces, Carats, and Grains The scale is for weighing primarily jewelery I believe.
If you put a nickel on it, it should weigh 5 grams. If it doesn't, then it isn't calibrated correctly. There should be a specific mode that you can recalibrate it on. I'd like to bid on this, so f/w. =)
Actually, a friend of mine did that last night and it is calibrated correctly, I didn't know anytning about it until I listed it here and I have learned so much since then, thank you for the info!