The App “APE Calculator” is for solving equations from non-linear optics. With over 10,000 downloads, it is one of the most frequently used apps for this purpose. The App is intended for customers and users, who are mainly concerned with non-linear processes of ultra-short pulse laser technology (UKP). It performs the relatively simple conversion of wavelengths into wave numbers or frequencies, but can also solve more complex tasks, for example, the dispersion caused by dispersion of short pulses. Users of OPOs or users of CARS also benefit from the rapid determination of pump, signal or idler wavelengths. The Calculator is available as a web application on the desktop (www.ape-berlin.de) or as an app for Apple and Android.