Cannot read 0 volts

I'm currently using the PicoLog 1000 series to test a relay circuit.

However, I have no way of measuring 0 volts. I can't ground it or short it to allow it to see 0 volts. It just jumps around between 0 and 2.5v. Any voltage above 0v works just fine. But the moment it hits 0, it jumps. And if I short it or ground it, the average voltage even RAISES.

This sounds as if you may have some grounding and connection issues. Can you please email details of your circuit and connections to support@picotech.com, and one of the hardware specialists will take a look for you.