The San Diego Air and Space Museum can’t afford to make any floor changes unless they notify volunteer docent Mark Carlson and his partner. A relocation here or there might throw them off course. Carlson is blind and his assisting partner is his seeing-eye dog, Musket. Carlson and Musket know the way around the place quite well. “I do the talking and he does the walking, easily working our way through early flight, golden age, the tri-motor, Phantom and the MiG-17,” Carlson said. The likable docent in the red coat is a wealth of information, having studied four months to enter the docent fraternity. “I like to tell the stories,” he said. He spent 100 hours learning what was there and obtained everything he could find on tape about the history of flight to fulfill guide requirements. “When I get in, I ask about any changes,” he said. “Maybe they’ve moved the Spitfire or Warhawk around. Then I go out there and use my foot and glove for location so Musket knows where they are. If you just lined up the Spitfire, the GB, Skyhawk and Jenny I could identify them. There’s an intimacy I have with these planes.” He laughingly compares his situation with an old joke about the parents of Helen Keller punishing her by changing the furniture. “I walk up to a group and tell them I’m their tour guide,” he said. “Then there’s a moment of dead silence. I’m sure there are a lot of raised eyebrows.” His moment of embarrassment might come when he’s describing something on a wall and a member of the tour group says, “I don’t think it’s there anymore.” That’s why he checks first about any surprises. A one-time graphics designer, Carlson has been legally blind for 10 years. He has a hereditary disorder called retinitis pigmentosa. His father and brother are also blind. Carlson, 48, lives in Carmel Mountain Ranch, near Rancho Bernardo and commutes by bus. “I take the No. 20 to town, transfer to the 7, get off at President’s Way and walk to the museum,” he said. “When my eyesight became really bad in the late ‘90s I decided I had to do something else,” he said. “I got some training in blind skills, like mobility, living trends, cane use and braille. I had to find a different line of work.” He worked seven years for an agency that specialized in technology for disabilities but was laid off. “So, my wife finally said, ‘Honey, can’t you find something to get out of the house on the weekends?’” Carlson said, “By then I had Musket, a male, yellow labrador retriever, to help me,” Carlson said. “People now say, ‘There’s Musket and what’s his name.’”