Cut the rind of a lemon being careful not to include the white of the lemon (you can make a spiral of the peel for better visual effect). Cut a slice of orange.
Pour some ice cubes (always an odd number) directly into a tumbler glass to the brim and stir with a bar spoon, so as to cool the glass evenly. Throw the water formed in the tumbler. Pour the Campari and Martini Rosso, completing everything with soda.
Mix well using a simple stirrer or straw and garnish with the orange slice. Finally squeeze the lemon rind around the edge of the tumbler, before laying it beside the orange. Serve immediately.