Hi Norm,
we can make the plot even thicker.
Your red label indicates that tire pressure is measured in 'atü'.
Depending on whether you rounded up or down, or used the conversion value for the 'technical' or the 'standard' atmosphere, you get slightly different values (see:
http://en.wikipedia.org/wiki/Technical_atmosphere).
1.8 'technical' atmospheres (at) = 25.60 psi
1.8 'standard' atmospheres (atm) = 26.54 psi
One should use the first value because 1.8 'atü means 1.8
at (not atm) above normal atmospheric pressure at sea level.
Late 280SL cars had a purple sticker that combined the metric pressure values (now in kp/cm^2) and 'psi' values in one label.
This label is still available from Mercedes: p/n 113 584 0039.
I have read some posts claiming that Merceds also used a black label for W113 cars where both units were combined but I am not sure whether this is correct. I have, however, seen a reproduction label in black in Germany once in a Pagoda. But that label is really remarkable since the metric pressure unit is stated as kp/cm^3 - force per
volume I doubt that Mercedes would make such a blunder!