I'm refining my measurements with the scope by grounding the probe nearer the point of interest. But I've measured a small voltage on the ground strip of solderless breadboards with the volt meter. The voltage is on the order of 50mV up to 150mV or more. It seems to me that it is OK to ground the scope probe there since my power supply and function generator are floating. But I'm not really sure. I know the probe's ground is connected to earth ground. Since it must be common practice can I get some feedback?