One source of confusion when discussing maths and computing is the direction of the Y-axis. In maths, on graphs, positive values on the Y-axis point upwards. So +10 is higher than +4. In computing, on screen displays, positive values on the Y-axis typically point downwards (0 on the Y-axis is the top of the screen, and values increase as you go down the screen), so +4 is higher than +10:
Although this sounds horrendously confusing, in practice it doesn’t make very much difference. It makes a difference to the inequalities (e.g. if you want to check if an actor in Greenfoot is above another, you check if the Y value is less), and it also makes a difference to angles: in maths, positive angles go anti-clockwise, but in computing, positive angles go clockwise. But apart from that, most other calculations are unchanged.
Some people like to argue for hours that one is more right than the other, but it’s just a convention (the X-axis could equally be reversed if we wanted), and although it’s irritating that we have two conventions, it’s not the end of the world.