The TC-324C and TC-344C temperature controllers (Warner Instruments, USA) provide power to a variety of heating devices including Warner heated platforms such as the microscope stage used here. Each channel supplies up to 22 watts into a load of 10 ohms. Heat setpoint was controlled automatically in Auto mode via thermistor feedback. A loop-speed selector provided three feedback speeds to optimize the thermal stability of the device being heated. Heat setpoint also could be manually controlled in Manual mode.