S15 stock boost gauge, why 2 boost measure units?

[Yakozan]

Just looked closer on the S15 boost gauge.
Why does it seem to have vacuum in "mmhg" and boost in "Kg/cm2"?
Why not just stick to one measuring unit or is it a industrial standard of some sort to measure vacuum in mmgh?

http://i15.photobucket.com/albums/a380/sushiming/S15/DSC00844.jpg

 

[Pazz]

Good question.

If my calcuation/conversions are correct 700mmHG = 0.933 Bar. So why they just didnt use kg/cm^2 or just bars is anybody's guess.

 

[Nicely]

My Autometer gauge I had in the S14 was like that too.