《Windows Graphics Programming Win32 GDI and DirectDraw》6.1节中有这样的描述：
The Windows NT/2000 graphics engine uses signed fixed-point numbers to represent coordinates, having a 4-bit fraction part and a 28-bit signed integer part. Points with negative coordinates or coordinates beyond the height or width of the device surface are considered clipped. So the maximum physical device size is 227 by 227, or 0.88 mile by 0.88 mile in 2400 dots-per-inch (dpi) resolution.
我自己算的方法是：2^27 / 2400 / 1000 = 559240.55
作者给出的是0.88mile，感觉很疑惑。