Step 1: Understanding hysteresis.
Hysteresis refers to the phenomenon where the response of a system depends not only on its current state but also on its past states. In measurements, this means that the data output may vary when measurements are repeated in different directions.
Step 2: Conclusion.
Among the given options, hysteresis is the phenomenon where measurements can be inconsistent based on the scanning direction, making it the correct answer.
Final Answer:
\[
\boxed{3. \text{Hysteresis}}
\]