I'm trying to make a matlab plot with two types of data, i.e. temperature and air flow rate. Since the temperature and air flow rate are on different scales I wanted two y-scales and since there are quite some data sets, I wanted to make the two air flow rates bold. I tried this, but it doesn't work: plotyy(time,reator_temperature_matrix,time,air_flow_matrix,'LineWidth',2) After a long journey, I ended up here: http://www.mathworks.com/matlabcentral/newsreader/view_thread/81078 And saw it solved the following way: [AX,H1,H2] = plotyy(time,reactor_temperature_matrix,time,air_flow_matrix) ; set(H2,'LineWidth',2) This solved my problem, though now I'm curious what [AX,H1,H2] means and I couldn't find it anywhere on the internet. What does '[AX,H1,H2] = ...' create? Can I choose any name for AX, H1 and H2? When I go to the workspace, I see three vectors with some numbers, but they don't make any sense to me.