<p>The amount of toner remaining in each toner cartridge (20a-20d) of a printer (1) is estimated by incrementing a count when one pel is detected in each small region of the bit map. The printer senses toner out, after which the scale ascribed to one count is revised to reflect the actual count to toner out. Specifically, the count to toner out becomes the number representative of empty so that one-half of that count is interpreted as half full. The remaining toner in each cartridge is displayed to the operator at a gauge (21).</p>