An open-loop on-line computer connection to a DTA apparatus of high time constant and the developed software for data acquisition and utilization are described. The new system was calibrated thermomentrically and calorically. The main aim is a enhanced purity estimation, especially by using of the modified Van't Hoff equation based on DTA curves, which first must be transformed to process-power-curves. Computer aided DTA provides utilization of higher quality and makes them faster and more exactly. Plotting of DTA curves which are baseline corrected and constructed as mean of equal curves as well as zooming are powerful and essential tools in optical comparison. The better estimation of the baseline under the peak and the computation of process-power-curve from DTA curve enable estimations based on curves of DTA apparatus' with high time constant as like as bases on DSC-curves.