| Particle Number Density Meter: This meter measures the number density of liquid or solid particles. You must attach the number density meter to an orange hotspot on the Ultrascope (see Ultrascope View (Freezing and Melting)). In the Properties Box of the number density meter, you can choose to measure the numbers of either solid or liquid particles. Be forewarned that the sudden change between solid and liquid at the phase transition recorded by this meter (and others) is not accurate. You must place an number density meter to plot number density using the graph tool.