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.
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.
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:
|Leaflet 1||155 mm|
|Leaflet 2||153 mm|
|Leaflet 3||155 mm|
|Leaflet 4||154 mm|
|Leaflet 5||156 mm|
|Leaflet 6||154 mm|
|Leaflet 7||157 mm|
|Leaflet 8||155 mm|
|Leaflet 9||155 mm|
|Leaflet 10||154 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.