These three sketches belong to two separate buffalo studies. The first sketch was achieved using wipe-out and the second one (in two parts) has been constructed using basic shapes for placement and 'weight'. I have recently found that my students have benefitted from this 'loose' way of measuring in order to achieve more accuracy and the correct sizing on a bigger format. I suppose you could call it a an informal way of gridding up without being too tight. We then use 'wipe-out' and line work to complete the artwork.