# Accuracy and quality control

## Accuracy

in textiles is the amount of acceptable variation from the specified measurement from which you can cut out pattern pieces, add or sew seams.

Tolerance is measured in + or - mm.

is the amount of material between the edge of the fabric and the seam, and it is tested to check it meets the tolerance stated in the .

### Example

A factory may say that a seam allowance of 20 mm is needed, with an acceptable tolerance of +/- 5%.

5% = 20 × 0.05

= 1

The seam can have a tolerance of 1 mm either side of the 20 mm.

20 + 1 = 21 mm maximum

20 - 1 = 19 mm minimum

If this were the case, then the seam allowance could range from 19 mm to 21 mm.

Question

A factory has specified that a seam allowance of 25 mm is needed, with an acceptable tolerance of +/- 8%.

What is the possible range of tolerance?

8% = 25 × 0.08

= 2

The seam can have a tolerance of 2 mm either side of the 25 mm.

25 + 2 = 27 mm maximum

25 - 2 = 23 mm minimum

The seam allowance can range from 23 mm to 27 mm.

## Quality control

During the manufacturing process, quality control (QC) checks are carried out - for example, to check whether:

• seams are sewn straight
• components are sewn on straight and strong
• fabric has no faults or misprints
• stitching is straight and neat
Quality control (QC) is the system of checks throughout the manufacturing process to make sure each step is completed to a high standard.

Although quality control checks can increase waste, with faulty products being thrown away, if a factory develops a reputation for being reliably high in quality, money is saved in the long term through products being reordered.

In a manufacturing flow chart, quality control checks are placed as decisions in diamonds to show where a step would need repeating if there was a mistake: