===Understanding the FDTD Observable Types===
In EM.Tempo, project observables are the simulation data that are generated by the simulation engine at the end of each simulation run. EM.Tempo's FDTD simulation engine calculates all the six electric and magnetic field components (E<sub>x</sub>, E<sub>y</sub>, E<sub>z</sub>, H<sub>x</sub>, H<sub>y</sub> and H<sub>z</sub>) at every mesh grid node at all time steps from t = 0 until the end of the time marching loop. However, in order to save memory usage, the engine discards the temporal field data from each time step to the next. Storage, manipulation and visualization of 3D data can become overwhelming for complex structures and larger computational domains. Furthermore, calculation of some field characteristics such as radiation patterns or radar cross section (RCS) can be sizable, time-consuming, post-processing tasks. That is why EM.Tempo asks you to define project observables to instruct what types of output data you want in each simulation effortprocess.
EM.Tempo offers the following types of observable (click on each type to learn more about it):
* '''[[Data_Visualization_and_Processing#Probing_Fields_in_Time_and_Frequency_Domains | Field Probe]]''' for monitoring E- and H-field components at a fixed location in both time and frequency domains