Hello ith.

How many grams is your scale able to wiegh? You can add a tray but dont make the tray a heavy object. Once you turn your scale on and place the tray on it , it will go into minus(-) to what it wieghs. Say if your scale was 200g scale and you placed a -50 tray on there and hit the tare or zero button. You could only way 150g before you have to calibrate your scale again. If you cant figure the math, give me what your tray wieghs and how much your scale can hold and Ill tell you a safe ammount to wiegh, unless of course you have 100gram weights to re cal.