In industry and mechanical engineering, drive belts are indispensable. The maximum lifespan of a drive belt depends on the optimal belt tension. A motor failure caused by belt damage can result in significant costs. To prevent motor and belt damage, regular checks of belt tension are essential. The belt tension of drive belts can be measured quickly and reliably with a digital belt tension measuring device. The pre-tension measuring device is particularly effective for checking belt systems through frequency measurement. The belt tension measuring device is an optical maintenance tool for determining belt tension. This pre-tension measuring device consists of a display unit and a sensor head. The sensor head of the belt tension measuring device is attached to a gooseneck. The movable gooseneck allows the sensor head to be positioned flexibly, enabling measurement of belt tension in hard-to-reach places. The belt tension measuring device measures the static tension and frequency of the belt when stationary. A small impulse on the belt is sufficient to set it into vibration. Thanks to its sensor, the belt tension measuring device captures the natural frequency generated and visualizes it on the large illuminated display. From the belt frequency and the optionally entered belt length and mass, the pre-tension measuring device can directly determine the tension force of the belt. With the belt tension measuring device, the user can determine the belt tension in the system of pulleys and take immediate action to adjust the tension to the desired value. Measuring belt tension requires high precision, and the pre-tension measuring device performs this quickly and reliably.