Measuring temperature of diced chicken
Here's a technical explanation as to what happened. An analog thermometer works on the principle that different metals expand more than others when heated. There is a bi-metallic strip in the pen part of the thermometer in the shape of a spiral coil, which is attached to a piece of metal which turns the pointer. The outside of the strip expands more when heated and contracts more when cooled than the inside, so when heated the coil will twist the pointer in the direction of the spiral. 



As the pen part of the thermometer heats up the coil changes shape and adjusts the temperature. As you can see from the picture the sensitive area of the thermometer is the length of the coil, that entire area needs to be heated up to the same temperature in order to read correctly. In your case what you were trying to measure was too small and had to compete against the ambient temperature of the air. 

Digital thermometers work on a different principle entirely, using an electrical device called a thermocouple on the end of a probe. 


The bead at the end is the actual sensor, and as it is much smaller it is therefore more precise than a bi-metal coil. However, I still think one of these wouldn't work because again the size of the meat isn't enough to heat the probe's sheath enough for the sensor to read correctly.