companies. A testimonial from Bud Dacus impresses tugboat engineers because Bud has worked the Mississippi for 25 years – longer than Mark Twain. Demonstrations are most effective when they compare your product’s performance with your competitors’. Try to devise a simple demonstration that your reader can perform himself, like inviting him to scrape the liner of your air-duct with a coin to see how tough it is. Testimonials work well when they come from recognized experts in well-known companies. News works well. It appears that readers scan the advertisements in technical journals looking for new products. To my surprise, a McGraw-