There is one method which may be useful to get better results.
Use a heater inside the calorimeter to keep the temperature at 50C or so. Measure the power needed to maintain temperature, this will show whether your circuit is generating or removing heat. And the bonus is that your calorimeter temperature is constant. Therefore your thermometers won't experience temperature change and their quirks won't affect the measurement.
An analogue is the electromagnetic balance scale, which keeps the scale platform at a constant position and instead measures the force needed to keep it there. This way the mechanical linkage of the scale sees no movement and therefore cannot affect the measurement. This was done in the past using galvanometers as the platform in order to measure extremely tiny weights.
Use a heater inside the calorimeter to keep the temperature at 50C or so. Measure the power needed to maintain temperature, this will show whether your circuit is generating or removing heat. And the bonus is that your calorimeter temperature is constant. Therefore your thermometers won't experience temperature change and their quirks won't affect the measurement.
An analogue is the electromagnetic balance scale, which keeps the scale platform at a constant position and instead measures the force needed to keep it there. This way the mechanical linkage of the scale sees no movement and therefore cannot affect the measurement. This was done in the past using galvanometers as the platform in order to measure extremely tiny weights.