Mark Lloyd wrote:
> The old electric stove my grandmother had had one burner that was
> thermostatically controlled. The other burners didn't have knobs, but
> rows of buttons (labeled something like "high", 'med-high", "medium",
> "med-low", "low", "simmer", "warm", "off").

GE and Hotpoint ranges of the 50s and 60s typically had dual coil
surface units with five switched heat levels:

High -- 240V across both coils in parallel
Second -- 240V across one coil
Third -- 240V across both coils in series
Low -- 120V across one coil
Warm -- 120V across both coils in series

The "infinite level" time regulated controls in modern ranges require
much less wiring than the old style (less cost) and provide more user
control.