In this chapter, the authors introduce an important concept in financial economics: the exposure of an individual stock to changes in the market portfolio. They introduce slider for sliding window functions, and furrr to apply mapping functions in parallel. However, instead, the developers want to perform the estimations of rolling betas for different stocks in parallel. If they have a Windows machine, it makes most sense to define multisession, which means that separate R processes are running in the background on the same machine to perform the individual jobs. Using eight cores, the estimation for our sample of around 25k stocks takes around 20 minutes.