three or four inches up ( 8 or 10 cm for those that have only one measuring system)
Technically, the standard is metres. This can be impractical, however, (0.08-0.1m) so mm should be used for smaller objects, seeing as cm shouldn't exist except when measuring volume (1cm^3 = 1ml) as the x10^3 scale goes mm, m, km, Mm, etc.
We generally ask you to convert inches to centimetres or millimetres because it makes it easier for people outside of the USA, Myanmar and Liberia to understand.
Surely it isn't too hard to do?