Printers occupy one of those areas of computing in which figures are all important. Splashed over magazine ads for the latest inkjet printer you'll see things like "2,400dpi!" or "10ppm!".

The situation is more complex than the figures suggest. More isn't necessary better and ultimately all you can judge a printer on is how fast it takes a page to appear and the quality of the printing when it does.

The technical side of printing fascinates some and bores others. Basically a printed page consists of tiny little dots which make up the image or letters that you see. In the case of an inkjet printer, these dots consist of coloured ink. In the case of a laser printer the dots are tiny particles of carbon which are sealed onto the paper by heat (ever wondered why your prints come out hot?).

The logic involved in printer advertisements is that if you can get more dots within a square inch then you can get more detail onto the page. The logic then dictates that more detail means more quality.

In the real world, a printer outputting at a mere 600 dots per inch may well produce better prints than one outputting 2,400 dots per inch (dpi). The reason is that there are many other elements at work, such as how accurately the software that controls the printer, known as a 'driver', can manage the printer. You also have to consider the paper handling mechanism, which works within fractions of an inch. And then there's the actual quality of ink or, in the case of a laser printer, the quality of the toner - poor quality ink lacks vibrant colours and won't react with the page in the correct manner, causing rough edges and long drying times. In the case of poor quality toner in a laser printer, the black areas won't be as dense.

If you want to purchase a printer then go along to your local PC shop and ask for a sample print. If the sales staff pull one out of a folder under the counter then be wary -- this will have been produced in ideal situations. They're not going to show you the 9 prints prior to that one which were rubbish. They'll also have printed onto top quality paper - laser printers can print on standard paper without qualms but inkjet printers print best on specially coated paper. Fair enough, you might think, but this paper is often highly expensive.

Ask to see the printer in action. Take along your own picture on a floppy disk and ask them to output it. By all means let them output it on the special paper but ask to see it printed on standard paper too, and see how well the printer copes - some printers will cope excellently whilst others will start to show serious weaknesses.

Also note how long the print takes to arrive in the output tray. Is it a matter of seconds or have you got time to make a cup of tea? How noisy is the printer whilst outputting? Is it whisper-like or more akin to busy traffic?

In the case of an inkjet printer, inspect the print that comes out. Look at how well the colours have been reproduced, and skin tones in particular. Watch out for the common problems of printing. The first is banding - visible lines on the print where the printer hasn't quite matched up one pass of the print head with the one lower down. Look out for 'dithering' too - sometimes the dots that make up the image are visible to the naked eye which can spoil the effect of a good print.

With a laser print, inspect the denseness of the black. Is it really black or more of a dark charcoal grey? (The same rule applies for text outputted by an inkjet printer, by the way). Are the letters perfectly formed when you look closely or can you see the 'computerfication' - jagged edges on descenders, for example.

With both a laser and inkjet printer, examine the page per minute output figures - how long will you be waiting for 10 pages to drop into the output tray? Ask the shop assistant to send twenty pages of text to the printer and time it to see if the quoted figures match reality. They rarely will.

Consider the running costs. How much do replacement ink cartridges cost? Or, in the case of laser printers, how much do replacement toner cartridges cost? Also consider the cost of the 'drum' in a laser printer, which will be replaced infrequently but is nonetheless part of the total running cost.

Watch out too for wide variations in the amount of pages outputted by a toner or ink cartridge. One company might sell a cartridge for £10 whilst their competitors sell theirs for £30 but it's likely the former will only print around 2,500 pages whilst the latter might print three or four times that.

Finally, take a good hard look at the build quality. Waggle a few things and see how well they're fixed down. On inexpensive printers this can be a serious issue. Be particularly diligent in examining laser printers because these often have to survive constant use in tough office environments.