What is the dangers of Global Variables in Drupal specifically?

Which variables are considered to be real variables (as opposed to nominal variables)?

• I know what real and nominal variables but i don't know any examples apart from money is nominal and output is real.

• Answer:

  That's the whole basis of the difference. Economists can relatively easily measure changes in any measurable bit of the economy in money terms - output, retail sales, stocks (in the US they call them 'inventories' although they're not invented), exports, etc. They can measure inflation - or disinflation - the change that's just a change of prices not of actual production or consumption - in the broad economy or in any category of goods or services. Then they calculate the real change by doing the maths. So the way to think is this. Anything that's bought and sold for money can be measured in money terms. The change in it is the nominal change. The real change is the same variable and the same database with inflation calculated and removed from the measurement.