I put it on for Katie to be honest, as she has mentioned etudes and their use and also said she struggles with string crossing. I used wohlfhart for my etudes, I have got kreutzer as well but all these etudes cover the same things more or less in my view.

Best way for string crossing is quite simple, play a long bow on g, and then stop , drop your arm round till you are on e,without making a noise then long bow on e, you roll the bow, from g to e, you then can do the same thing with other strings, for some reason this works, dont ask me how, muscle memory? works though.;) saying that you will still hit other strings now and again, which is why on fiddle, you always, no matter how advanced, have to practice these exercises, something which I am guilty of not doing.