GU image size advice is wrong

[Alan Bell]

http://developer.ubuntu.com/api/ubuntu-12.10/qml/mobile/resolution-independence.html

"For example, if the destination size of the bitmap is 10 gu * 10 gu and the developer targets a Smart Phone (1 gu = 18 px) and a laptop (1 gu = 8 px) then he/she only needs to create a bitmap of 144 px * 144 px to support both devices."

this doesn't make sense. 18*8 might well be 144 however that is irrelevant. The image in question would be upscaled to 180x180 for the smartphone and downscaled to 80x80 for the laptop. 144x144 is not a good starting point for either.

As a unit the GU isn't very well considered, it is different sizes on a 7inch tablet vs a 10 inch tablet at the same resolution, it could be bigger or smaller on a phone than on a laptop, there is no set number of GU that fits on a screen. It kind of combines the problems of pixels with the problems of points. I can see the benefit of there being a device appropriate unit of smallness, the width of a "thin" line on each device or some fraction of the size of normal text that a human would like to read, but this seems a funny way to reach that objective.

[Juhapekka Piiroinen (juhapekka-piiroinen)]

The documentation says before that sentence:
"We require that for each bitmap the developer provides the highest resolution version of it. The system will perform a high quality downscaling of the bitmap when needed on lower density screens."

So more looks like a typo and the proper value should be 180x180px, instead of that 144x144px.