A long metric/imperial thread on the Australian Woodworking forum
included a discussion on the best way of marking a metric tape. The
fact the the marks at 5mm were slightly longer than the other 1mm
marks (but shorter than the 10mm marks) was considered a plus point.
I have just bought a Starrett 6"/150mm metric conbination square. I
was surprised to find that there are four heights of marking (longest
to shortest):
10mm, 5mm, (2,3,7,8)mm, (1,4,6,9)mm. Or, IOW, extra prominence is
given to the markings at 2,3,7,8 mm position within 10mm.

Anyone know why?
I have the feeling that they would have preferred to have marked 2.5
and 7.5, following imperial practice! Even odder, two of the four
edges have 1/2 mm as unit, so markings at 2.5 and 7.5 would have made
some sense there!
(and please, no wars. . .)