A unit (1) for carrying out a first operation and a second operation onto a first area (2d, 2e, 2f) and a second area (2a, 2b, 2c) of a packaging material; first area (2d, 2e, 2f) and second area (2a, 2b, 2c) being spaced for a first distance (e) along direction (A) when a portion (20) of packaging material comprising first area (2d, 2e, 2f) and second area (2a, 2b, 2c) is flat; unit (1) comprising: a feeding group (6) for feeding a web (3) of packaging material along a direction (A) and in a first sense; a first tool (28a, 28b, 28c) adapted to carry out first operation on first area (2d, 2e, 2f) arranged in a first desired position; a second tool (27a, 27b, 27c) adapted to carry out second operation on second area (2d, 2e, 2f) arranged in a second desired position; first (28a, 28b, 28c) and second tool (27a, 27b, 27c) being spaced for a second distance (d) along direction (A); feeding group (6) comprises: advancing means (10, 16) controllable to arrest web (3) in a position, at which second area (2a, 2b, 2c) is spaced for an intentional offset (X) from second desired position; and actuating means (50) controllable for moving second area (2a, 2b, 2c) towards second desired position, so as to recover offset (X); the absolute value of the difference between first distance (e) and second distance (d) being equal to offset (X). (Figure 5)