[StavrosK]

"Oh wow, air pressure fell to almost zero, a person would suffocate in ther... Wait a minute, the ground unit is 940! This is a 6% difference!"

[zaroth]

Sometimes ground units reflect ground truths, even if the scale doesn't actually hit zero.

[thomasahle]

Yup, this is also why I like the metric version. With inches of quicksilver it's hard to know where zero is.