Here is a list of mistakes you can do using PerfExpert, and how to fix them.


During calibration, at the final step, the application refuses to validate the calibration.

At the final step (the ninth), you are asked to put the phone in any position (angled preferably) so that PerfExpert can verify the calibration quality. If this fails, it means that one or more calibration steps was not performed correctly.

For successful calibration, use a horizontal and a vertical plane. For example, a table and a rectangular box that allows a right angle with the table (as described in the Guide). Be sure to fully secure the phone before the end of each step count downThroughout the calibration time (when the text "Calibration..." is displayed on the screen), the phone must be completely stable.

Do not perform a calibration when the phone battery is too hot, such as when you just unplug your phone charger. It is also best to avoid a calibration when the battery level is too low.

My calibration is recent, and yet in my measures, PerfExpert displays a warning of poor calibration.

In addition to being susceptible to wear, accelerometers are also susceptibles to temperature. Smartphones accelerometers are generally not temperature compensated. So in case of variation in temperature since the calibration time, it can no longer be valid, even if it was made 15 minutes before, at home.

When this happens, currently the only solution is to repeat a calibration on site, under the same temperature conditions.


After pressing the START button, the clock triggers by itself before the car takes off.

The acceleration threshold for triggering the timer is too low, the clock is too sensitive and can be triggered if the measured car is highly vibrant. You have access to the Trigger setting in the Preferences menu from the main screen. Gradually increase the trigger until you no longer have this problem. Typically, a value of 0.1G (or 1.0m/s²) works very well for most cars.

After pressing the START button, the clock doesn't trigger when the car takes off.

Conversely, you entered a too high Trigger value. In this case you should ideally go back to the default value (0.1 G). The goal is to have the smallest possible value that does not trigger the clock before the real take off of the car.

PerfExpert fails to retrieve weather data.

The weather data retrieving system rely on the Network location system and the internet connection of your phone. If one of the two is not available then the weather data retrieving will fail.

Check that your phone is not in airplane mode and that you have a good network connection. If your phone connects to the Internet only in WiFi (and therefore no internet available at your test site) before you disconnect from your wireless access point to move to your test site, be sure to launch the application once to bring weather data retrieving. We consider that the weather data are valid for a measure if it does not date from more than 2H.

In all cases, you can always enter your own weather data by checking the box "Enter values manually" in the Preferences screen.