Appendix 3—figure 1. Triangle translation changes its radial elongation.

Triangle is translated by $\mathrm{\Delta }\overrightarrow{r}=\overrightarrow{r}(t+\mathrm{\Delta }t)-\overrightarrow{r}(t)$. Although the triangle elongation did not change during the translation, the radial component of the triangle elongation changes due to the change of radial direction by $\mathrm{\Delta }\phi$.