This is a benign one, but that could trouble beginners :

in http://processing.org/learning/examples/mousesignals.html

bvals[width-1] = 255;

should be replaced with

bvals[width-1] = height;

to remain coherent.

And if you want to tidy up the rest of the code,

xvals[width-1] = mouseX;

could be fine tune into

xvals[width-1] = mouseX*height/width;