Potters & Sculptors - Making Rock from Mud
Catherine - 999 is simple, but probably not what you want to choose for a heating ramp because it could shorten the life of the elements in some kilns which don't have a protective over-ride to avoid excess heating element temperature. But it's a convenient programming notation for cooling ramps.
When you specify a 999 ramp during a heating or cooling ramp, the actual rate achieved is obviously going to be quite different to what you specified. It simple means heat as fast as possible or cooling without added heat.
Our kiln is relatively overpowered relative to its size, so a 999 ramp is actually a 999 ramp until it heats up to about 1,600 F when it starts to slow down to a real ramp of about 670 per hour, and above 2,000 F it's slower still. Our empty kiln could complete a Cone 6 firing within about 2 hours and 40 minutes. With ware in the kiln it would probably take a little longer, but it would still heat up quick enough to crack and break much of the ware in the kiln.
We use auto-fire pre-programmed firings in our kiln controller. See page 24 of the Bartlett Genesis Kiln Controller to see the firing profiles Bartlett uses in their kiln controllers. PDF file here -- Genesis Kiln Controller - (see page 24)
Slow-cools are added onto the firing with additional buttons like a microwave oven. A nice toy to add to a kiln for $329 Bartlett Genesis Controller or you can buy their earlier V6-CF model for $219.
Bartlett Genesis kiln controller
Bartlett V6-CF kiln controller
The older RTC-1000
requires you to program each firing every time, yet costs $219 just like the more capable V6-CF