1. Control Charts for Attributes
p chart (fraction of nonconforming items)
np chart ( number of nonconforming items)
c chart (number of nonconformities in some unit)
u chart (number of nonconformities per unit)

2. The p Chart Procedure
Step1. Gather the data. Select the size, frequency and number of samples.
Step2. Calculate p for each sample.
Step 3. Set the scale for the control chart.
Step 4. Plot the p values and connect them.
Step 5. Calculate p-bar, and the control limits after about 20 points have been charted.
Step 6. Interpret the chart

3. Chart Interpretation
Shifts. A shift of seven or more points to a higher or lower level could mean that something has affected the proportion defective or that the definition of what is defective has somehow changed.
Trends. A run of seven or more points up or down indicates that something is causing the proportion that is defective to change in a gradual manner, poorly trained operators, different inspection criteria, or poorly controlled parts in the assembling process.

4. The np Chart Standard given: UCL = np0 +3np0 (1-p0)
LCL = np0 - 3np0 (1-p0)
No standard given:
UCL = x + 3  x (1- x/n)
LCL = x - 3  x (1- x/n)

5. The c Chart Standard given UCL = c0 + 3 c0 LCL = c0 - 3 c0
No standard given
UCL = c + 3c
LCL = c - 3c

6. The u Chart (variable unit size)
u = c/k k is the number of inspection
units in each sample
UCL = u0 + 3 u0/k
LCL = u0 - 3 u0/k