A fluid properties measurement apparatus for use with a conventional high temperature high pressure test cell includes a load cell assembly and a drive motor that drives a rotating shaft magnetically connected to a vane assembly having multiple vane elements, wherein the motor rotates in response to reactive forces of a fluid sample and the load cell assembly measures reactive forces of the sample. In one embodiment, a stepper motor allows for precise shaft rotation. A method of measuring fluid properties includes frequent measurements throughout a complete rotation cycle of a vane assembly within a test cell. A system interference profile is generated which identifies stress variations resulting from various system components throughout the cycle. Measurements of a sample's fluid properties are likewise performed to obtain a profile. Comparison of the sample profile with the interference profile provides fluid properties measurement independent of stress variations resulting from various system components.