value of reduced temperature equal to that of reduced pressure?

I only know that a pure gas at same reduced temperature and reduced pressure will have same compressibility factor.
But I wondered is this correct? value of reduced temperature equal to that of reduced pressure?
from
http://www.answers.com/topic/law-of-...ponding-states


One more question,from wiki "In order to obtain a generalized graph that can be used for many different gases, the reduced pressure and temperature, and , are used to normalize the compressibility factor data. " What is the experiment? and How to draw the generalized graph ?
from
http://en.wikipedia.org/wiki/Compressibility_factor

THANK YOU