Hi it is one of the best and useful apps that I have seen. Unfortunately it crashed after updating 1 mar 2016. Correct it pls. It dosent start. I installed it two times but it has a problem in starting it gives you a black or white screen. I am so dissapointed for loosing such magnificent app. Fix it please. The most important problem in this app is " there is no instructions to define the possitive directions in coordinate for plot and decide the directions of momentum, shear and normal forces in a text " so u make mistakes in answers in possetive or negetive and the time for answering also is too short. Thanks a lot
