I had my students make a sun compass as part of a land navigation lab... and had to make accomodations as teenagers typically didn't wear a watch, and those that did, it was invariably a digital watch not analog. I had them use a drawing compass so they would get a good pivot point, and make the radius as large as possible (3x5 card)...protractor to get good 3,6,9,12 quadrants and try to make good "dot" marks at 15,30,45 minute tics between hours... since we are north of the Tropic of Cancer, the sun is always behind us facing north, so have them hold a thin stick/straw/twig on edge of circle, rotate card so shadow falls across the center pivot point and across the analog hour hand location coinciding to the time from their cell phone or digital watch (to nearest 15min)...north is 1/2 way between the shadow line and 12 o'clock...you might print up a good copy, and attach it to a mirror back with clear packing tape....have them practice/compare with an orienteering compass...