At this point two performance indices that have been derived: for tension σ / ρ {\displaystyle \sigma /\rho } and for bending σ / ρ {\displaystyle {\sqrt {\sigma }}/\rho } . The first step is to create a log-log plot and add all known materials in the appropriate locations. However, the performance index equations must be modified before being plotted on the log-log graph.