Complex sentence: Digital camera sales peaked March 2012 at about 11 million a month, but sales have declined significantly ever since and by March 2014 about 3 million were sold each month, about 30 percent of the peak sales total.
Split into simpler sentences: Digital camera sales peaked in March 2012 averaging about 11 million units a month, but sales have declined significantly ever since. By March 2014, about 3 million were purchased each month, about 30 percent of the peak sales total.