... points(pressure$temperature, pressure$pressure) lines(pressure$temperature, pressure$pressure/2, col="red") points(pressure$temperature, pressure$pressure/2, col="red") With ggplot2, you can get a similar result... their primary resource for research, problem solving, learning, and certification training Preface www.it-ebooks.info | xi Safari Books Online offers a range of product mixes and pricing programs... Handbook logo, and the O’Reilly logo are registered trademarks of O’Reilly Media, Inc R Graphics Cookbook, the image of a reindeer, and related trade dress are trademarks of O’Reilly Media, Inc Many