This graduation thesis shows the impact of temperature changes on digital level. The first and theoretical part explains the method of geometric levelling and its equipment, especially the digital levels and bar code levelling staff as well as the errors in levelling. The second part is practically orientated and consists of three tests. Firstly, changing the instrument's temperature is non-linear to the temperature of the level. Besides, the level takes 2,5 times longer to heat up than to cool down. Secondly, the impact of temperature changes in the surrounding air on the horizontal line of sight is greater when they happen closer to the instrument and lesser when they are nearer the levelling staff. Thirdly, the readings from a level that is cooling down are very dispersed, a clear sign that before any work is to be done, a level's temperature needs to be brought to the temperature of the surrounding air first
