An attitude heading and reference unit coupled to a display device of an avionics system, the attitude heading and reference unit comprising: a primary processing device and a secondary processing device both included within a single modular unit; a primary inertial sensor assembly configured to produce primary inertial data; the primary processing device communicatively coupled to the primary inertial sensor assembly, wherein the primary processing device is configured to receive the primary inertial data and calculate a primary set of attitude and inertial solutions from the primary inertial data using a primary set of algorithms; a secondary inertial sensor assembly configured to produce secondary inertial data; the secondary processing device communicatively coupled to the secondary inertial sensor assembly, wherein the secondary processing device is configured to receive the secondary inertial data and calculate a secondary set of attitude solutions using a second set of algorithms, wherein the primary set of algorithms is different than the second set of algorithms and the secondary processing device is configured to calculate a subset of the attitude and inertial solutions that the primary processing device calculates; and wherein the primary set of attitude and inertial solutions and the secondary set of attitude solutions are output from the attitude heading and reference unit to the display device, wherein the display device is configured to: determine when a first attitude solution from the primary set of attitude solutions is different than a second attitude solution by a first threshold, wherein the second attitude solution is produced by an inertial reference unit (104A/104B) other than the attitude heading and reference unit; use an attitude solution from the secondary set of attitude solutions as a discriminator attitude solution, wherein the first attitude solution, the second attitude solution, and the discriminator attitude solution are each the same one of pitch, roll or heading measurements; wherein the display device is further configured such that: if the difference between the first attitude solution and the second attitude solution is greater than the first threshold, then the display device is configured to determine whether the primary set of attitude solutions is correct by determining whether the difference between the first attitude solution and the discriminator attitude solution is less than a second threshold or whether the difference between the second attitude solution and the discriminator attitude solution is less than the second threshold. a primary processing device and a secondary processing device both included within a single modular unit; a primary inertial sensor assembly configured to produce primary inertial data; the primary processing device communicatively coupled to the primary inertial sensor assembly, wherein the primary processing device is configured to receive the primary inertial data and calculate a primary set of attitude and inertial solutions from the primary inertial data using a primary set of algorithms; a secondary inertial sensor assembly configured to produce secondary inertial data; the secondary processing device communicatively coupled to the secondary inertial sensor assembly, wherein the secondary processing device is configured to receive the secondary inertial data and calculate a secondary set of attitude solutions using a second set of algorithms, wherein the primary set of algorithms is different than the second set of algorithms and the secondary processing device is configured to calculate a subset of the attitude and inertial solutions that the primary processing device calculates; and wherein the primary set of attitude and inertial solutions and the secondary set of attitude solutions are output from the attitude heading and reference unit to the display device, wherein the display device is configured to: determine when a first attitude solution from the primary set of attitude solutions is different than a second attitude solution by a first threshold, wherein the second attitude solution is produced by an inertial reference unit (104A/104B) other than the attitude heading and reference unit; use an attitude solution from the secondary set of attitude solutions as a discriminator attitude solution, wherein the first attitude solution, the second attitude solution, and the discriminator attitude solution are each the same one of pitch, roll or heading measurements; wherein the display device is further configured such that: if the difference between the first attitude solution and the second attitude solution is greater than the first threshold, then the display device is configured to determine whether the primary set of attitude solutions is correct by determining whether the difference between the first attitude solution and the discriminator attitude solution is less than a second threshold or whether the difference between the second attitude solution and the discriminator attitude solution is less than the second threshold.