Print this page at 100% / actual size (any small scaling error is fine – it is the same for every piece). Cut out one card, lay a piece in the middle and scan. The scanner finds the black frame and uses it to correct the perspective and to measure every piece in millimetres, which makes matches more reliable.
Use a dark card for light pieces and a light card for dark pieces. Keep the card flat and the piece inside the inner area.
Print check – this line should be 50 mm long: