# Specifying Observables

The Observables Frame Palette by default is not displayed with the other BioNetGen windows, however it may be selected for display from the View menu Observables Palette. Prior to simulation execution, the user should specify which products are to be saved as outputs using this palette.

During simulation of the reaction network all products are determined, along with their resultant concentrations, however a small number of moderately complex reaction rules may generate a large number of products. Biomolecule interactions are an example of a complex adaptive system and exhibit a large degree of combinatorial complexity. To tame this complexity, use of the Observables Palette allows the user to specify only the product biomolecules that are of interest, by selecting each and dragging to the Observables Frame Palette. BioNetGen will acknowledge this registration as a valid pattern. During simulation of the network, any products that match this pattern are then saved for later viewing into the output files.