Accuracy and quality control

Consistency and quality are very important to a manufacturer who wants to offer the customer the best product. No product is made exactly the same, but an acceptable tolerance, or range of difference, can be controlled when a product is being manufactured.

If a photo frame has to be made to hold an A4 certificate, the frame must allow for the A4 paper to fit neatly inside. A4 paper is 297 × 210 mm. In this example, if the frame is inaccurate by +/- 1 mm, then this could still be acceptable. This range of measurement is called the tolerance - in this example the tolerance would be shown as 297 × 210 +/- 1mm.

Some products need to be more accurate than others. A complex pop-up card might be made to a tolerance of +/- 0.1 mm, whereas a simple pop-up card could be made with a tolerance of +/- 1 mm. It is important for designers to know the tolerance so that they can calculate the upper and lower limits.

Example

A quality control check is carried out on a random sample of greetings cards - each should be made with a tolerance of +/- 1 mm.

The length of the card is meant to be 195 mm and the first greeting card measured is 197 mm in length. This is 2 mm too long and so is outside the 1 mm tolerance.

Question

A quality control check is made on a random sample of leaflets. Each leaflet should be 155 mm in length +/- 1mm.

Below shows a table of the lengths recorded of a sample of ten leaflets:

LeafletsLength measured
Leaflet 1155 mm
Leaflet 2153 mm
Leaflet 3155 mm
Leaflet 4154 mm
Leaflet 5156 mm
Leaflet 6154 mm
Leaflet 7157 mm
Leaflet 8155 mm
Leaflet 9155 mm
Leaflet 10154 mm

How many leaflets were out of tolerance and should not be used, and which leaflets are they?

Two leaflets were produced out of tolerance. These were leaflet 2 and leaflet 7.

Companies will put quality control procedures in place to ensure the products are produced to a high standard and no errors occur. In printing, a registration mark is used, which can be looked at to ensure the printing lines up with the paper - this prevents the person from having to look at the whole product to check for errors.

A perfect registration mark, showing each of the CMYK colours (cyan, magenta, yellow and black) alligned aside an off registration mark where the colours have shifted.

Crop marks are used to show where to cut on a sheet of paper, and colour bars are used to check that the colours are being printed to the correct consistency and intensity.

A white sheet showing print elements, corner and crop markings and colour bars.
Sheet with colour bars around the outside and crop marks in the corners - registration marks and colour bars are always placed outside of the crop marks so that they do not interfere with the main print