**How to Interpret a Control Chart?**

control chart

**Remark:**It is based on the Normal Distribution.

**SPC Trend Rules**

**Rule#1:** A single point beyond either control limit

Uses: Detects very large/sudden shifts

False alarm rate: 0.27%

**Example:**

SPC Trend Rule#1

**Rule# 2:** 9 consecutive points on the same side of the centerline

Uses: Detects small shifts or trends

False alarm rate: 0.39%

**Example:**

SPC Trend Rule#2

**Rule# 3:** 6 consecutive points steadily increasing or Decreasing

Uses: Detects strong trends

**Example:**

SPC Trend Rule#3

**Rule# 4:** 14 (or more) consecutive points are alternating up and down.

Uses: Detects systematic effects, such as alternating machines, operators, suppliers, etc.

**Example:**

SPC Trend Rule#4

**Rule# 5:** 2 out of 3 consecutive points at least 2 std dev beyond the centerline, on the same side

Uses: Detects large changes

False alarm rate: 0.30%

**Example:**

SPC Trend Rule#5

**Rule# 6:** 4 out of 5 consecutive points on the chart are more than 1 std dev away from the CL

Uses: Detects moderate-sized changes

False alarm rate: 0.53%

**Example:**

SPC Trend Rule#6

**Rule# 7: **15 (or more) consecutive points are within 1 std dev of the CL

Uses: Detects a decrease in process variation

**Example:**

SPC Trend Rule#7

**Rule# 8: ** 8 (or more) consecutive points are on both sides of the CL, but none are within 1 std dev of it.

Uses: Detects an increase in process variation

**Example:**

SPC Trend Rule#8