Boxplots are a great way to visualize interquartile ranges and their relation to the median and the overall distribution. These graphs display ranges of values based on quartiles and show asterisks for outliers that fall outside the whiskers. Boxplots work by splitting your data into quarters....
So, we cannot take scale = 2, because this makes the decision range too inclusive, meaning it results in too few outliers. In other words, the decision range gets so big (compared to 3σ) that it considers some outliers as data points, which is not desirable either....