[Chuck Schwark]

The dial is a celluloid acetate plastic called Tenite, introduced to the industry in 1929. I warps very easily with temperature and age. It cannot be easily flattened. If the warp does not interfere with the rotation, I'd leave it alone. I've heard others that get a small flattening by pressing under some weight in a warm environment. I suspect this would take a long time with minimal success.

Tenite has a temperature of deformation much lower than other newer plastics, so storing any Tenite plastic in a hot attic say, over time, will warp it. The cellulose plastic also has an affinity for moisture absorption, again causing warping, like a damp basement or garage or barn. Aging effects in the chemical makeup of the Tenite also contribute. At the time Tenite was a cheaply produced platic that could be easily moulded and given "swirly" effects. It was not meant to be perfect 50-60 years later.

See the Mystery Control section of my site for more info.