Thanks for the replay,
Given the orientation of the board, as shown in the picture I attached, is correct, tilting the nose of the platform on which the board is mounted forward and down should give negative values. Tilting the platform backwards should give positive values.
In one of my setups I’m using the IMU board onboard a vessel. The compass and roll is correct, but the pitch give negative values when the vessels bow are going up, and positive values when the bow goes down.