Nautilus Inc., just days removed from a precipitous plunge in its stock price, appeared to have found level ground Tuesday. The Vancouver-based exercise equipment brand ended the day on the New York Stock Exchange at $6.86 per share. While that was nearly 42 percent lower than its $11.79 closing price Thursday, it was just two-tenths of a percentage point below its opening price of $7.07 Tuesday morning, the week’s first day of trading after markets were closed in observance of Martin Luther King Jr.