relative vs. absolute

[Victor]

Perhaps I am overly influenced by mathematics and physics jargon, but I
am having trouble figuring out in what sense "relative" is being used in
a piece on "absolute hardness". Normal interpretation of "[measure] X
[for Y] is relative" for me is that X is a measure of Y where Y is being
compared to Z. If a "scale" merely gives some ranking of Y, Z and other
"stuff", I would never consider describing such a scale as "relative".

In the example here, I would consider the "absolute hardness" scale to
be relative, in the sense that the tool that measures it, a sclerometer,
does so by effectively comparing the test hardness to some reference
measure. But the Mohr scale is simply a rank ordering of minerals in
terms of hardness without any attempt to relate them, so using
"relative" in this context makes no sense to me. And I don't just make
that distinction in English--hopefully it's not some form of early senility.

Do I need to get out more or is the following passage really odd with
respect to its use of "relative"? My guess is that the author of the
piece reinterpreted the modifier "absolute" to apply to "scale" rather
than to "hardness" and recovered his meaning of "relative" from there.

http://www.inlandlapidary.com/user_area/hardness.asp

Absolute Hardness
The Mohs Hardness Scale is relative. Fluorite at 4 is not twice as hard
as gypsum at 2; nor is the difference between calcite and fluorite
similar to the difference between corundum and diamond. An absolute
hardness scale looks a little different than the relative scale. Using a
piece of sensitive equipment called a sclerometer, a comparison of the
absolute hardness of minerals can be measured. Most minerals are close
in hardness. But as hardness increases, the difference in hardness
greatly increases as seen in this  absolute hardness scale.

Using an absolute scale you can say that corundum is actually 4 times
softer than diamond, not half as soft as Mohs relative scale leads you
to believe.

Mohr's Scale: 1. Talc, 2. Gypsum, 3. Calcite, 4. Fluorite, 5. Apatite,
6. Orthoclase/Feldspar, 7. Quartz, 8. Topaz, 9. Corundum, 10. Diamond
Absolute Hardness Scale: 1 Talc, 3 Gypsum, 9 Calcite, 21 Fluorite, 48
Apatite, 72 Orthoclase/Feldspar, 100 Quartz, 200 Topaz, 400 Corundum,
1600 Diamond

------------------------------------------------------------
The American Dialect Society - http://www.americandialect.org