Cnfusion: Are gas valves simply on/off?

Hi folks:

The more I look into various PID configurations the more confused I get. I am setting up a gas-fired single vessel system. In the mash step the PID needs to (of course) control the temperature. Does the pid simply cycle the gas on and off, or does it actually cause an adjustment to the gas flow rate?

I guess what I am asking is... For this PID:
http://www.auberins.com/index.php?main_page=product_info&cPath=1&products_id=106

Or this one:
http://www.auberins.com/index.php?main_page=product_info&cPath=1&products_id=3

Would I be using the "on-off" control mode or the fuzzy PID mode? Sorry if thisis a dumb question... Something about this just isn't clicking for me yet.

-Blake

its not variable, its on or off when controlling gas. Youll also want to use the on-off control method.