Want a house shot picture?
Grab a pen and a sheet of paper.
Draw 2 parallel lines about 1cm apart and 10cm long.
Grab a highlighter and draw a 78cm line down the middle.
That's your oil pattern
Variance on highlighter thickness and line length pretty much covers every centre!
Hehehe..... Oh yes it does.
That's the THS graph drawing 101 class.