Portable device for contactless measurement of a size, such as the diameter, of small and medium sized objects, such as wires, bars or tubes, even in movement, which comprises a light beam generator (1), two light beam deflector elements (2, 4) located opposite each other, a measuring region (3), an enlarging lens (5), a light beam splitting device (6). The light beam is split into two parts to form two separate images of the object (14) to be measured, being perceived by two linear image sensors (7.1, 7.2) and processed by two electronic circuits (8.1 and 8.2) and by an electronic processing component (9).

A comparative measuring tool, including: a storage unit; an input device; a measuring device; and a display device. The input device is configured to allow a user to perform function selection, deviation limit setting, and reference value adjustment; the measuring device is configured to capture a relative displacement and transmit the relative displacement to the storage unit; the display device comprises a display screen configured to show real-time data including the relative displacement, deviation limits, and a reference value.