“What is the volume of an object with depth a and radius z?”/“Pi z z a.”

A popular mathematical pizza joke that has been printed on posters is:
 
Q: What is the volume of an object with depth a and radius z?
A: Pi*z*z*a.
 
The joke has been cited in print since at least 1997.
 
 
Google Groups: rec.puzzles
pizza + anarchy (spoiler)
NickGard
9/19/97
(...)
Silly ObPuzzle:  My local pizza delivery company is called Perfect Pizza.  This means that not only do the pizzas taste perfect but they are also perfectly circular and perfectly uniform in depth.  They’ve just delivered a pizza with depth a, and radius z.  What is its volume?
 
Twitter
Larry Kyrala
‏@coldnebo
groan: What’s the volume of a pizza with radius z and depth a?
5:00 PM - 27 Feb 2009
 
Twitter
mijj
‏@mijj
a pizza with radius Z and depth A has volume PI*Z*Z*A : ref reddit user Benjaminsen http://is.gd/13uEp
9:51 AM - 16 Jun 2009
 
Slashdot
Re:4 whole pieces? (Score:5, Informative)
by Beardo the Bearded (321478) on Tuesday December 15, 2009 @02:02PM (#30447278)
(...)
Someone on /. has a sig that said:
 
A pizza with depth a and radius z has a volume of pi z z a.
 
Today I Found Out
THE MATHEMATICAL VOLUME OF A PIZZA IS PIZZA
March 12, 2010 Daven Hiskey
Today I found out that the mathematical volume of a pizza is pizza.  How does that work you say?  Well if z = radius of the pizza and a = the height then Π * radius2 * height = Pi * z * z * a = Pizza.
   
reddit
If you have a pizza with radius “z” and thickness “a”, its volume is Pi(z*z)a (i.imgur.com)
submitted April 1, 2014 by BuzzBorn
 
BuzzFeed
The 24 Greatest, Nerdiest Jokes Ever Told
Supercollider? I hardly even know her!
posted on Jun. 16, 2014, at 4:25 p.m.
Tanner Greenring
(...)
6. What is the volume of an object with depth a and radius z?
PI Z Z A