original_query: What is a macro-level model and why is it time-consuming and labor-intensive to create?
query: What is a macro-level model in prognostics and why is it time-consuming and labor-intensive to create?
answer: In prognostics, a macro-level model is a mathematical model at the system level, showing the relationship between system inputs, states, and outputs.  It's a simplified representation, which can lead to faster prototyping. However, for complex systems (like gas turbine engines), creating a macro-level model is time-consuming and labor-intensive due to the system's complexity.