how to center the screen, in processing

center.pde

// how to center the screen in processing. I have the hardest time remembering, much less intuiting, this:

size( 200, 200 );

int l = 0;
int b = 70;
int r = 500;
int t = 700;

float xres = width/float(r-l);
float yres = height/float(t-b);

scale( xres, -yres );
translate( -l, -t );

line( l, b, r, t );