We calculate the height of the current column in the graph by using our old friend the map() function (from section 3.2.2). Then we call drawColumn() to draw the column. We then call drawColumn() with zero so it will draw an empty column after the one that was just drawn. This gives a visual indicator of where we are. Lastly we increment xChart so that we will be at the next spot in the graph next time we come here. Most of the new stuff is in our drawColumn() function. This takes a value
which is the “height” of the line to draw. The idea of the function is to quickly add “full” segments of 8 and then calculate the size of the last segment