c-Chart (Defect Count)
The c-chart monitors the number of defects per inspection unit (defects per PCB, paint flaws per car). Assumes a constant sample size.
Single-column CSV (defect_count) or paste defect counts per batch
In paint surface inspection, each panel has a fixed area and the total count of bubbles, scratches, and particles is recorded per panel. The c-chart is ideal for defect counting on fixed inspection units, e.g., flaws per roll of fabric or alarms per machine. With a c-chart, quality engineers can quickly detect process deterioration (a sudden rise in defect counts) and take preventive action before customer complaints occur.
Defect counts of 5 samples: 3, 7, 2, 5, 8 c̄ = (3+7+2+5+8) / 5 = 5.0 UCL = c̄ + 3×√c̄ = 5.0 + 3×2.236 = 11.71 LCL = max(0, c̄ - 3×√c̄) = max(0, 5.0-6.71) = 0 → All samples are within control limits → If the next panel shows 12 defects, an out-of-control alarm is triggered
FAQ
Related Tools
p-Chart (Defect Rate)
The p-chart monitors the defective rate (pass/fail per unit), while the c-chart monitors total defects per unit. Choose based on how quality is defined.
Open toolControl Chart (X̄-R)
Attribute charts (p/c-chart) suit defectives and defects; variable charts (X̄-R) suit continuous data such as dimensions and weight.
Open toolFailure Mode & Effect Analysis
The c-chart shows defect counts; FMEA helps predict and prevent defects in advance, serving as an upstream planning tool for SPC.
Open tool