The sketchbook...
.. that I always carry with me and in which I draw more or less every day. It's a practice booklet for me to tighten up my Obervativerbatim. Sketching helps me to estimate proportions and distances and to quickly incorporate the ability to develop movements in me. I draw on purpose with a pen so I can't make corrections. This way I get 'feedback' directly from the pen, without the intervention of an eraser...
There is still a long way to go... on the way to my ultimate goal!