Legal for trade is a designation placed on scales which have obtained NTEP certification in accordance with 

the U.S. National Institute for Standards and Technology (NIST) Handbook 44 for having locked calibration 

that ensures that the scale is accurate and not tampered with.

If you plan on using your scale commercially in the U.S., you should only use legal for trade scales. If you plan 

on using your scale non-commercially, then a "not legal for trade" scale should suffice.