A drill drills holes with standard deviation of depth 0.05 cms and mean depth of holes is 5.70 cms. Find 3 σ control limits for mean of samples of size 4. Given A = 1.500.
Given: X̄1 =5.70 cms :
σ1 =0.05 cms, n=4
The 3σ – control limits for X̄ – chart (standards are given) are
C.L = X̄1 = 5.70
L.C.L = X̄1 – Aσ1
= 5.70 – 1,5 × 0.05 = 5.625
U.C.L = X̄1+ Aσ1
= 5-70 + 1.5 × 0.05
= 5.775.
