Infant scale recommendations

I have an infant scale sling customer looking for a good hanging scale for weighing newborns. She's willing to buy either a digital or mechanical scale. She tried this mechanical scale from In His Hands, but it failed on two points:

• the hook was too small to hold both rings on the infant scale sling
• it didn't zero out (tare) to account for the weight of the sling

I'd like recommendations for a good hanging scale that goes up to 12-15 lbs, shows increments of 2 oz or less, zeros out, and can hold a pair of aluminum rings. (The last thing is negotiable, since you could always attach a larger "S" hook or carabiner to the scale hook.)

Thanks for your help!

Red Bloom infant scale sling with red rings