So I got a Antminer U3 and have been toying around with it.What mining difficulty should I set it to? (Slush's pool)
For smooth sailing, set it to a minimum of the hash rate in Gh/s. Considering it's a 63Gh/s device (if you're lucky), 64 will do nicely. If you set it lower you get more shares at lower difficulty but you're also putting unnecessary load on the servers. If you set it higher you get fewer shares at higher difficulty but the variance apparent at the pool side will be higher. It'll even out over longer stretches of time, regardless, but if you prefer smoother graphs, stick with the aforementioned.
please could you tell me the diameter and the hight of the U3
Gen 2 (Wire cage): 120mm diameter, 82mm height
No idea about the Gen 1 (Cylon case), doesn't seem like I kept figures around for it.