Yeah, atan will only give results over a range of angles (I forget, either just 0-90 or 0-180) which is kind of inconvenient if you want to measure an angle which is actually 270 degrees. Still, the C++ runtime library has a function called 'atan2' which works out the quadrants for you, which is what Construct uses. If you ever need atan2 for something else, I think angle(x, y, 0, 0) is equivalent to atan2(y, x). But the x,y and 0,0 might be the other way round. Can't remember.
Other way around: angle(0, 0, x, y)
Old post I know, but was searching for atan2 and found this. Thanks!