Hey Ducobot - a 970 mm reading for a 925 mm target is usually caused by measurement conditions rather than the factory calibration itself. The published 1–2% figure is based on a controlled setup, in practice, accuracy depends a lot on target texture, lighting, distance, whether you measure the center vs. an edge, and stereo settings.
To improve accuracy, please check our stereo-depth tuning guide here, there are few steps you can do to make it more accurate: Configuring Stereo Depth. Our depth accuracy page is here as well: Depth Accuracy.
Also you could also do Manual Calibration, which if done well, can improve the depth.
Thanks,
Oskar
