“But these go to 11…”

This scene in Spinal Tap captures something fundamental about data scales and labeling, but what is it?

The buyer wants to know if the amp with knobs scaled from 0-11 is louder than those with settings from 0-10.

I’m not sure if the more important message is:
1) In the face of numeric data people still believe what they want
OR
2) If you translate units of measure, re-index values or change scales you can intentionally or unintentionally confuse your users.