Hi. There's a bug in the tutorial. It says sig.connect(&print_sum); sig.connect(&print_product); sig.connect(&print_difference); sig.connect(&print_quotient); prints The sum is 8 The difference is 2 The product is 15 The quotient is 1.66667 when in fact it prints The sum is 8 The product is 15 The difference is 2 The quotient is 1.66667 because slots are called in FIFO order. Regards, Bruno