Garmin Ltd. is having trouble finding its way in the era of hand-held mobile devices. Shares in the company, the biggest maker of GPS-based navigation aids, slumped 9.4 percent, the most on the S&P 500, after quarterly earnings fell 22 percent. The company was particularly hurt by slumping demand in its main automotive business. The shares fell the most in more than three years. Garmin also forecast 2013 sales and profit that would miss analyst estimates.