Without a better way to test it I ran it till empty, thumped it, banged it, ran it again, pulsed it, thumped it again and again etc etc. I didn't however disassemble the burrs..... I then weighed 25.1 grams of beans in, ran it, pulsed it etc 25.1 came out........took about 8 seconds of grinding I couldn't believe it, so I tried again This time repeat process but weighed 25.0 in, wouldn't believe it but 25.6 out 🙂 ....... There must be some retention within the burrs but it's not too bad I'm guessing......... Won't know till I pull them apart which I will do in a month or so. Build quality is as good as mazzer SJE was, and burr removal looks the same (collar looks identical) apart from a tab you depress as you unwind the collar (locking tab)..... So slightly more fiddly but still not bad If anyone lives near me at camden and wants a try they are more than welcome to come round and grind away.