Beckmann thermometer can not be used to measure temperature. It can measure only change in temperature.
The Beckmann differential thermometer
It is used for measuring small temperature differences, having readability of around 0.001°C. It was invented by the German chemist E. O. Beckmann in 1888. The range of temperatures measured with such a thermometer is determined by the amount of mercury in the reservoir and the thermometer’s capillary. Beckmann’s thermometers are used in laboratory practice for calorimetry and measurements near phase transition points, but their use decreases.
