Methods and systems accurately determine an analyte concentration in a fluid sample. In an example embodiment, a receiving port receives a test sensor. The test sensor includes a fluid-receiving area for receiving a fluid sample. The fluid-receiving area contains a reagent that produces a measurable reaction with an analyte in the fluid sample. The test sensor has a test-sensor temperature and the reagent has a reagent temperature. A measurement system measures the reaction between the reagent and the analyte. A temperature-measuring system measures the test sensor temperature when the test sensor is received into the receiving port. A concentration of the analyte in the fluid sample is determined according to the measurement of the reaction and the measurement of the test sensor temperature. A diagnostic system determines an accuracy of the temperature-measuring system. The calculation of the analyte concentration may be adjusted according to the accuracy of temperature-measuring system.