Px4flow updates image information at 400Hz or 250Hz?

As the question I ask in the title, could someone tell me px4flow updates the image at 400Hz or 250Hz?

I´ve found somewhere says it is 400Hz (in the User Guide PX4) and others show that it is 250Hz (in the paper named “An Open Source and Open Hardware Emedded Metric Optical Flow CMOS Camera for Indoor and Outdoor Application” by ETH Zürich).

Could you tell me which one is right?