Sentence:  First I make preliminary watercolor sketches in quarter scale ( <WSD>approximately</WSD> * * f inches ) in which I pay particular attention to the design principles of three simple values - the lightest light , the middle tone , and the darkest dark - by reducing the forms of my subject to these large patterns . 
Meaning of the word marked with <WSD> tags:  (of quantities) imprecise but fairly close to correct