Engine temperature

[Mustang]

My es78 reports my engine temperatures as being well above the Thermostat opening temperature. The thermostats are fully open at around 155° (measured with an accurate infrared thermometer at the Thermostat housing) while the mfd reads 215°. At those temperatures I would expect the engine alarm to be blaring. The water coming from the telltale is warm, not at all hot.
Is there a way to calibrate it to get reliable info? I am now questioning the accuracy of the other engine data (rpm, fuel flow, hours, etc.) I got this unit to take the place of all the guages due to limited dash space and need to be able to rely on it.