Monroe's engineers have developed the best available universal twin-spool ribbons for calculators, the Monroe P65M. This ribbon will fit every Monroe calculator model. Monroe pushed every envelope when designing a ribbon with the highest inking degree on the market and eliminated the risk of ink smudges. Monroe has even developed a true red ink that is extremely rich in color and used exclusively by Monroe, unlike the orange tint you see in watered down versions from other hands. To maintain the darkest print on their paper tape, users of Monroe products are suggested to change their Monroe P65M ribbons after replacing 3 paper tape rolls.