I have two industrial ovens which were made about 40-50 years ago and had the old knob-adjustable thermostat-type controller similar to what most refrigerators have. The problem was that both ovens eventually had trouble regulating the temperature. Moreover, I had to rely on the setting indicator for the inside temperature as there was no actual thermometer in the ovens.
What I did was to buy two, identical PID type digital temperature controllers and added my own Type-K thermocouples (one for each oven) to change these ovens into a modern, digitally-controlled oven. The controller I chose even had an RS485 interface for programming from a laptop. I had to buy an RJ45 jack for that and an RS485 to USB interface for my Windows-10 laptop. The old thermocouple controllers were removed, and replaced by the new PID controllers, along with new Type-K thermocouples to sense the inside oven temperature.
One benefit is that the Digital controller display provides LED readings for both the SET TEMP and the ACTUAL TEMP. There's also an LED to indicate when the heating element is powered on. Programming was easy and they work great. The amount of temperature ripple due to the on/off nature of the temperature control was vastly improved from about +/-20 degrees F to a low +/- 5 degrees F with the new controllers.
Installation wasn't too bad as these PID controllers run off of 120 VAC, 60 Hz power and have isolated relay outputs for the heating element. Since the heating elements take about 12-15 Amps at 120 VRMS, they needed a second, larger relay or contactor as the controller's internal relay rating was only about 1 amp.
Adjustment of temperature is as easy as using a digital home thermostat with buttons for temp up and down.
Anyone with an oven using an old knob-adjustable controller should consider updating there oven with a modern PID type. The cost of the controller's for a good brand was only about $ 120 each and I've seen similar units (possibly not as good on quality) for as low as about $30 on Amazon. The change was well worth my investment in both time and money.
