My July 16 Flying Tip discussed vertigo and how insidious a hazard it can be. Dennis Doyle of Tahoe Turbines in California responded with his own tip -- a sort of 'poor-man's synthetic vision' that uses your imagination instead of a computer database. Doyle wrote that he has been flying since 1965 and developed his technique "quite by accident." I'm not sure what he means by that. Maybe I should find out what's behind the story. He said that since most of his flying is in California sunshine, when he does encounter IMC, it can come as a shock to the system. What Doyle does, is to mentally transfer all he had been seeing on the ground to the surface of his artificial horizon. He wrote, "Look at the instrument as a pictorial of what you were looking at a few minutes earlier. Imagine the lines on the ADI to be roads and highways, picture towns and cities sitting there between the lines, and I guarantee the Vertigo will disappear as quickly as your ability to imagine."