As I said (somewhere) before, I didn't find the function description of CreateContext() to be very useful. But you guys have revealed some extra clues so I should be able to get on with it - thankyou very much.
Thomas (regarding another thread I started) - Maybe, out of all Amigas it's just mine that has weird zooming windows but... Startup the calculator program, move the window, click the zoom gadget and tell me what happens next. And don't get me wrong, I appreciate your feedback.