ECEFast represent ASL who manufacture automatic AC bridges for temperature measurement.
ASL supply a series of reference thermometers, each series being an order of magnitude higher in accuracy than the previous.
ASL have the technology to achieve extreme accuracy, and thus the lower accuracy and lower cost models are detuned versions of higher accuracy models.
The pinnacle of the range is the F900 reference thermometer which is used by National Standards Laboratories in many countries to define the degree C. This model has an accuracy of 20ppb or 5 millionths of a degree C.
There is a full range of accessories to allow channel expansion and integration into laboratory systems.