If you have to choose between Printer A which promises 16 ppm and Printer B that offers 24 ppm and both have the same price, which one will you buy assuming both are equally respectable brands? If you said "B", you may end up with a printer which actually has a ppm lower than 16.
Many consumers were not even aware that several printer manufacturers were fooling them all this while using the ppm trick.
An average printer customer, I include myself in that category, would generally look at the ppm or Page Per Minute speed of the printer for comparison between two makes. Common sense would dictate buying the one which offers the highest ppm so that you can print faster. And how did customers came to know about the term ppm?
Well, ppm was the term that all companies were, and are, using to advertise their printers. And there was a competition to outspeed the rivals by promising relatively higher speed. The trick was to state the "maximum ppm". How did they do this?
Simple. They defined their own page. So, if a manufacturer defined his "page" included only 15 lines and no images, his ppm would appear relatively higher. If another manufacurer decided to act more ethical and assumed that a typical real world A4 page would have a text of 25 lines and would include at least one chart or a graphic, their resulting ppm speed would appear lower. That would be a competitive disadvantage. This is how a ppm-war started among the printer brands.
But now there is a speedbreaker in the form of a new ISO standard on printing speed. The ISO/IEC 24734 standard defines the ppm and ipm (image per minute) for back and colour prints in a default single sided mode. The ISO standard allows customers to do an apple to apple comparison.
Cannon, Epson, Kodak, HP and Lexmark were the companies that worked with the International Standards Organisation to develop the standard. ISO ppm was finalized last year.
So, when you buy a printer next time, find out if the brand has signed up to ISO ppm and follows ISO ppm guidelines to state the real ppm.