Thermal technology works by creating an image from the small difference in temperature of each object living and nonliving. Each object produces or contains heat energy that is emitted in a form of infrared light, the thermal sensor detects this way the same way a digital camera detects light. The image is displayed on a screen or saved on a recording device.
Thermals are available in a number of HZ ratings, this is the refresh rate of the screen, the human eye is said to detect around 24-26HZ, so anything above this is fluid in appearance, refresh rates at 7.5-9Hz generally produce a choppy image without fluid motion.
Resolution is also important; 320x240 384x288 640x480 this is simply the number of pixels available on the sensor, the higher the resolution the higher the level of detail available and the higher the cost, around the 320x240 or 384x288 is considered the optimum for value for money and performance.