First of all, in layman's terms, a PID controller takes a set point, then checks the process temperature. It then figures out how long to keep a heating, or cooling source applied in order to reach the set point, without overshooting. As the process temperature gets closer to the set point, the heat ON vs. OFF time decreases.(Is this still in layman's terms?) Say you have a cycle time of 10 seconds, the controller will decide how close to the  set point the process temperature is, and figure out if it needs to heat for 3 seconds, and  be off for 7 seconds, or if the temperature is increasing too fast, and it only needs to be  on for 2 seconds, and off for 8, then repeat the cycle again.

These controls have a tendency to be very pricey, so the search was on for an affordable source for this as well. After checking a few local sources, I was very discouraged by the prices I was seeing. I ended up looking at Omega Engineering, and requested their Handbooks and Encyclopedia, which is part catalog, and part information. I was very surprised to receive 6 hard bound books absolutely free. I located a controller, in their  catalog with an option for 4 remote set points for $230. This unit, part# CN7630-4SP works very well!

I picked up an Omega PID controller on Ebay for about $60, so that now controls the HLT temp. You can see it in the very crappy picture up top.