These photos show the drop in electrical resistance when you pour liquid nitrogen on the YBCO. Here is the before at 1.3 ohm:
After liquid nitrogen:
As a point of reference, the lowest the meter goes when the clips are connected together is 0.5 Ohm.
Frost forms from the extreme cold:
Prometheus Fusion Perfection 
*NEGITIVE* 1.8 ohm? How is that even possible — either the coil is acting as a generator, or your meter is broken?
I’m guessing it’s just not zero’d correctly.
Stuart says that these meters are only accurate to 12 ohms or so.
It is like a percentage.. No meter can be 100% accurate. We know (at least theoretically) that resistance is zero. The meter might show different values, and even show variations in time. Polymeters (the tool he was using) usually have tolerances of +/- 15 ohm. Wich is very good for the use they are designed for.
Cheers!
It just indicates there was a charge build-up and thus a little current flowed in the opposite direction. Next time, short the cables together when you pour the liquid nitrogen on, and keep them that way a short while until the temperature is somewhat stable, and then connect up your DMM.