Computer-assisted measurements of plant growth with Linear Variable Differential Transformer (LVDT) sensors- A system is described which allows to measure plant growth with a high precision (-2 pm) and high frequency ( 1 measurement per sec). It is based on LVDT sensors and driven by a dedicated computer with a software that allows to perform almost immediate out-line data analysis and treatment. The software automatically controls the position of each sensor for optimal measurements over elongation of 15 cm with respect to the plant by triggering motors that lift up the LVDT' s. Twelve LVDT sensors channels with 4 environmental sensors (temperature, relative humidity and light intensity) monitor the plant growth and environmental conditions. The floral stem growth of Arabidopsis thaliana has been followed in a photoperiod of L:D 12:12 and then followed by continuous light. L: 0 synchronizes the stem extension rate, with the highest growth rate in the light phase. In continuous conditions, fluctuations of high and low rates persist with a period of ~24 h. This property is typical of a system under control of the biological duel. At another time scale (hours) stem extension rates measurements present oscillations, with an ultradian periodicity (~30 min). These examples illustrate well the large dynamics capacity and resolution of the developed installation.