Just for example I want to verify a weighing scale 150kg capacity 0.05g accuracy. If this are my test wts calibration result (20kg each) : 19.996, 19.996, 19.993,19.994 and 19.990, If I am going to verify the scale to 40kg, so I am going to add the results of two test weights as reference 19.996 + 19.996=39.992kg? or 19.99 + 19.99=39.98kg? which of this reference were correct 39.992kg or 39.98kg ? should i include adding the last digit?