The manual shows: ( UCL = \bar\barX + A_2 \barR ) and ( \sigma = \frac\barRd_2 ) It explains that ( A_2 ) and ( d_2 ) are constants found in a reference table (included in the appendix).
: A 7-page guide focusing on basic operation, switching the machine on/off, and fault rectification. Viewable on Scribd . sigma control basic manual pdf top