Here we advise on how these devices are described in terms of size. Information given by manufacturers and retailers on TV and computer screen sizes are another example of unfriendly practices that take advantage of dual measures.
Conventional and flat screen sizes
There are now two types of display device on the market and there is a slight variation in the way they are described.
Conventional – the cathode ray tube
These are the bulky devices that have formed the basis of TV picture displays since its invention. The screen size is usually given as the overall size of the of the tube measured diagonally across the front face – in inches.
This is not the viewable screen area!
When the CRT is enclosed in the TV or monitor casing the front face will be partially obscured. Hence the size of the actual picture will be smaller than this.
In the above example the tube size is the length of the white line between points X and Y, whereas the viewable screen size is the shorter diagonal (shown in red) between A and B.
Sometimes the viewable screen size is given but often in centimetres.
The headline figure for the TV set is given by the CRT size in inches with the visible screen size in cm, which obscures the difference!
In other cases the viewable screen size is given in inches as well but it is important for retailers to move in the direction of all metric product descriptions. Overall dimensions are often in cm as in the above example.
This is a good thing but mixing inches and centimetres for describing the same product is totally illogical and unhelpful to the potential purchaser.
If the seller only quotes the size in inches then demand it in cm as well as the visible screen size in the same units. Make it known that you want honest data in in metric only units for a sensible comparision.
Flat screen
Flat screen technology is gradually replacing CRT but some old habits die hard. There a number of competing variants LCD, TFT and Plasma but in terms of marketing they share a common practice.
In the case of flat screen the viewable screen size is the same as the overall size of the device itself. Unfortunately they are still being given in inches. So in such cases ask the dealer for sizes in metric. This will enable comparison between the viewable area of CRT and flat screen alternatives and gain a better understanding of the space saving in terms of overall dimensions.
UK Metric Association 