I see your 30cm and raise you 50cm.
(And I really dislike a ruler design that does not have measured markings right up to the end.)
Scales that have the measured markings to the end are not accurate since the end can be damaged. (Lesson from my mechanical drawing class back in the late 1970s)
I can see this possibility on a drawing table where such accuracy may be an issue if damage is not noticed. It is a valid perspective.
But damage is usually visible and rulers whose ends are exactly aligned with the last measure marks can be got into awkward 3D spaces to get accurate measurements, and sometimes you need to use the other side/end of the ruler, to get the measurement.
We’ve had plenty of trains and boats and planes - and buses, but not enough lorries…
HP 8470
@SamSam Was 8470 on the laptop/in the picture? Please do help me out here if it was. (Still, I guess it’s not technically against the rules.) 
8475
“Air Velocity Transducers”
I could check wikipedia or something, I guess…
but somehow I feel too tired to investigate what these are right now.
