  We present visual calculations in special relativity using spacetime diagrams
drawn on graph paper that has been rotated by 45 degrees. The rotated lines
represent lightlike directions in Minkowski spacetime, and the boxes in the
grid (called "light-clock diamonds") represent units of measurement modeled on
the ticks of an inertial observer's lightclock. We show that many quantitative
results can be read off a spacetime diagram by counting boxes, using a minimal
amount of algebra. We use the Doppler Effect, in the spirit of the Bondi
k-calculus, to motivate the method.
