As you will see in the schematic of chapter 4 the fixed temp switches vary two voltage combinations (that you get “for free” with split phase power) and two coils to get the limited power levels. But this requires multiple coils per burner as noted. If it’s a single nichrome element per burner then even with fixed detents it may likely use a bimetal switch.
> I assume it's changing the resistance.
This isn’t feasible since you would need a resistor that was as big as the burner and essentially dropped as much heat as a stove element - for instance you would need a dummy load to dump as much waste heat as the burner itself to get a medium setting.
In theory one could use a variac or multitap transformer - but again those would be relatively huge and heavy for the currents involved.
> I assume it's changing the resistance.
This isn’t feasible since you would need a resistor that was as big as the burner and essentially dropped as much heat as a stove element - for instance you would need a dummy load to dump as much waste heat as the burner itself to get a medium setting. In theory one could use a variac or multitap transformer - but again those would be relatively huge and heavy for the currents involved.