Local store could be found with a 800W light dimmer, it is good to go with a test if temperature control is able to be fun.
galss thermometer, having thermal reading as oven door leakage, almost 130*C
the DIY temperature logger is accurate as the comercial product does, at least this case of 180*C target, easy to expands if we will go for PID control and multi channel data logger. Cost is minimum but extraordinary performance and capable for expansion to meet individual needs.
so here is initial experimental data for target 180*C and control knob tuning of light dimmer for desired temperature, full scale at 10, very steep of temperature raise, almost steady about at 4 – 5 of knob scale to seeing 180*C, remember a very low cost light dimmer uses TRIAC & RC for firing angle adjustment to control how many electricity allowed pass to heater, AC current is sine wave product in 60Hz, so knob adjustment would not be achived in linear mode.
two heaters of this oven was being connected in series, spot welded, if cut, the heater will be over loaded with 110V or burn out very soon, not be able to cut away to control each heater on this simple way.