$($a$)$ Variability is present in any manufacturing process. No two products are exactly alike because of slight differences in materials, workers, machines, tools, and other factors. These variations can be classified into two categories.

Differentiate between these two causes of variation in the manufacturing process?

$[10$ Marks$]$

Statistical process control methods extend the use of descriptive statistics to monitor the quality of products and processes. The most commonly used tool for monitoring the production process is a control chart.

$($b$)$ Explain why control charts are important in quality management and how the X$-$bar and R charts are used to improve quality in an organisation?