Measuring Performance Properly
Estimated Lesson Time: 45–55 Minutes
Lesson Overview
In the previous lesson, you created your permanent benchmark flight. That flight now provides the foundation for every future performance test you perform.
The next step is learning how to measure performance correctly.
Many Flight Simulator users only look at one figure:
Frames Per Second (FPS).
Although FPS is important, it tells only part of the story.
A simulator running at 60 FPS can feel significantly worse than one running at 50 FPS if the frame delivery is inconsistent.
Professional optimisation is about understanding all of the performance data available—not just the headline FPS number.
In this lesson you’ll learn how to measure, interpret and compare the key performance metrics used by professional reviewers and performance engineers.
Lesson Objectives
By the end of this lesson you will understand:
Average FPS.
Minimum FPS.
Maximum FPS.
1% Lows.
0.1% Lows.
Frame Times.
Frame Pacing.
MainThread limitation.
GPU Limited status.
How these measurements work together to describe real simulator performance.
1. Average FPS
What Is Average FPS?
Average FPS is the average number of frames your graphics card renders each second during the benchmark.
For example:
During a benchmark your simulator may render:
58 FPS
60 FPS
62 FPS
59 FPS
The average might be:
60 FPS.
Average FPS provides a useful summary of overall performance.
However, it does not tell you whether the simulator was smooth.
Why Average FPS Can Be Misleading
Imagine two benchmark results.
Benchmark A
Average FPS:
60
Smooth from start to finish.
Benchmark B
Average FPS:
60
Large stutters every few seconds.
Both produce the same average FPS.
Only one provides a pleasant experience.
Average FPS tells you how many frames were produced.
It doesn’t tell you how consistently they were delivered.
2. Minimum FPS
Minimum FPS records the lowest frame rate reached during your benchmark.
This often occurs:
- During taxi.
- At busy terminals.
- During approach.
- While scenery loads.
- During rapid camera movement.
Minimum FPS helps identify the most demanding moments of the flight.
Why Minimum FPS Matters
Low minimum FPS may indicate:
- Heavy scenery.
- CPU bottlenecks.
- GPU bottlenecks.
- Asset loading.
- Temporary stutters.
It should always be interpreted alongside the rest of your benchmark data.
3. Maximum FPS
Maximum FPS records the highest frame rate achieved during the benchmark.
This often occurs:
- During cruise.
- Over open water.
- At high altitude.
- Looking away from airports.
Although interesting, maximum FPS is usually the least important performance metric.
A simulator that briefly reaches 180 FPS isn’t necessarily smoother than one that remains consistently at 70 FPS.
Consistency is far more valuable than occasional peaks.
4. 1% Lows
What Are 1% Lows?
1% Lows represent the average performance of the slowest 1% of frames rendered during the benchmark.
Instead of looking at the single worst frame, this metric measures the performance during the most demanding moments.
This makes it much more representative than simply recording the minimum FPS.
Why 1% Lows Matter
Imagine:
Average FPS:
90
1% Low:
38
Although the average appears excellent, the simulator regularly experiences significant drops.
These drops are often what the pilot actually notices.
Professional reviewers place great importance on 1% Lows because they reflect consistency under load.
5. 0.1% Lows
0.1% Lows measure the very slowest fraction of frames.
These usually represent:
- Large stutters.
- Asset loading.
- Shader compilation.
- Background interruptions.
Because they focus on extremely rare events, they help identify serious performance problems that may not affect the average FPS.
Should You Chase Better 0.1% Lows?
Not necessarily.
Occasional loading-related events are normal.
Instead, look for repeated poor results that occur consistently across multiple benchmark runs.
6. Frame Times
What Are Frame Times?
Rather than measuring how many frames are rendered every second, frame times measure how long each individual frame takes to render.
Measured in milliseconds (ms).
Example:
60 FPS
≈16.7 milliseconds per frame.
120 FPS
≈8.3 milliseconds per frame.
30 FPS
≈33.3 milliseconds per frame.
Frame time is often a better indicator of smoothness than FPS.
Why Frame Times Matter
Imagine two systems.
System A
Every frame:
16.7ms
16.6ms
16.8ms
16.7ms
Extremely consistent.
System B
10ms
28ms
14ms
23ms
Average FPS may be similar.
However, System B feels noticeably less smooth because frame delivery is inconsistent.
7. Frame Pacing
Frame pacing describes how evenly frames are delivered to the monitor.
Good frame pacing means each frame arrives at a consistent interval.
Poor frame pacing means some frames arrive quickly while others arrive much later.
This creates:
- Judder.
- Micro-stutters.
- Uneven camera movement.
Why Frame Pacing Is More Important Than Peak FPS
Many users chase the highest FPS possible.
Professional optimisers prioritise:
- Stable frame pacing.
- Consistent frame delivery.
- Predictable performance.
A stable 60 FPS often feels smoother than an unstable 80 FPS.
8. MainThread
Earlier in the course, you learned that Microsoft Flight Simulator is frequently limited by the CPU’s MainThread.
During benchmarking, Developer Mode may report:
MainThread Limited.
This means:
The CPU is preparing frames more slowly than the GPU can render them.
The GPU is waiting for the CPU.
Increasing GPU power alone is unlikely to improve FPS until the CPU bottleneck is reduced.
Recording MainThread status during every benchmark helps explain why performance changes between scenarios.
9. GPU Limited
If Developer Mode reports:
GPU Limited.
The graphics card has become the limiting component.
In this case:
Reducing GPU-intensive settings such as:
- Resolution.
- Clouds.
- Reflections.
- Ambient Occlusion.
may improve performance.
Understanding whether your benchmark is CPU-limited or GPU-limited is essential before making optimisation decisions.
Bringing It All Together
A professional benchmark looks at all of these metrics together.
For example:
Average FPS:
72
1% Low:
61
0.1% Low:
54
Frame Times:
Stable
Frame Pacing:
Consistent
MainThread:
Occasionally Limited
GPU:
95–99%
This tells a far more complete story than simply saying:
“My simulator gets 72 FPS.”
Common Mistakes
Looking only at Average FPS.
Ignoring Frame Times.
Ignoring Frame Pacing.
Comparing different benchmark flights.
Recording only one benchmark run.
Assuming higher FPS always feels smoother.
Student Exercise
Today you’re going to complete your first professional benchmark.
Step 1
Load your permanent benchmark flight created in Lesson 2.
Use exactly the same:
- Airport.
- Aircraft.
- Parking Stand.
- Weather.
- Time of Day.
- Graphics Settings.
Step 2
During the flight, record:
FPS
- Average FPS.
- Minimum FPS.
- Maximum FPS.
- 1% Lows (if available).
- 0.1% Lows (if available).
Frame Analysis
- Frame Times.
- Frame Pacing.
Performance Bottlenecks
- MainThread Status.
- GPU Limited Status.
Step 3
Review your results.
Ask yourself:
- Was the simulator smooth?
- Were frame times consistent?
- Was the GPU or CPU the limiting factor?
- Did your 1% Lows stay close to your average FPS?
- Were any stutters reflected in the data?
Step 4
Save your benchmark results.
These measurements will become the reference point for every future optimisation throughout the Performance Academy.
Student Checklist
Average FPS recorded.
Minimum FPS recorded.
Maximum FPS recorded.
1% Lows recorded.
0.1% Lows recorded.
Frame Times reviewed.
Frame Pacing assessed.
MainThread status recorded.
GPU Limited status recorded.
Benchmark saved.
Lesson Summary
Congratulations.
You now understand how to measure simulator performance like a professional.
Remember:
- Average FPS is only one part of the performance picture.
- Minimum FPS, 1% Lows and 0.1% Lows reveal how the simulator behaves during demanding moments.
- Frame Times measure how long each frame takes to render, while Frame Pacing shows how evenly those frames are delivered.
- MainThread and GPU Limited indicators help identify the true performance bottleneck.
- The most enjoyable Flight Simulator experience comes from stable, consistent performance—not simply the highest possible FPS.
- By recording all of these metrics together, you can accurately evaluate whether an optimisation has genuinely improved your simulator.
Knowledge Check
- Why is Average FPS alone an incomplete measure of performance?
- What information does Minimum FPS provide?
- Why are 1% Lows often considered more useful than Minimum FPS?
- What do 0.1% Lows typically reveal?
- What is the difference between Frame Times and Frame Pacing?
- What does a “MainThread Limited” message indicate?
- What does “GPU Limited” mean?
- Why should all of these metrics be considered together when analysing benchmark results?