I got one question for you: which are the factory codes for this type of printer - HP PSC 1510. Usually there is a code (press the buttons in a special sequence) which makes the printer output a statistics (number of pages printed, the ink level, its serial number and so on).
Well, I’ve contacted the HP and surprisingly, I got the answer.
So, in order to output a factory test page, you have to press and hold the cancel button and then press the color copy button. Release the two buttons. The printer will output the test page. On that page, beside all the other codes, which meaning so far I don’t understand, there is a code named ‘PG’. The value assigned to that code is the number of pages printed. Of course there are also all sorts of other statistics: the ink level, serial numbers (cartriges and printer), the other codes I don’t understand (most of them that is ) etc.