Abstract: A trowel (10) is equipped with an optical detector (13) that detects a laser beam (12). The optical detector (13) may be arranged detect the laser beam (12) only when aligned with the laser beam (12). The trowel (10) provides feedback to the user when it detects the laser beam (12) and when it does not. The feedback may be a sound, a light or a haptic feedback. When the trowel (10) is used for constructing a tapered floor, such as in a bathroom, the laser beam (12) may be originated from a laser level (40) arranged on a support (30). The support (30) is positioned inside a floor drain (32), for example a bathroom floor drain (32).