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It seems like I have a problem with understanding the values I am getting from the accelerometer and gyroscope.

First of all, it is stated that the IMU is using a left-handed coordinate system where Z is directing upwards. (as mentioned here : ... 1572880735) page number 10

However, I get +1 in the Z direction when the board is standing still ? I thought I should get -1 as the accleration is in the negative direction ?

I thought that the sensor may be flipped upside down ( so one axis will be flipped while the other stays the same) but both of them are still flipped which does not make sense ?

The gyroscope are following the (right hand rule ) even for a left coordinate system ?

any help would be appreciated. Thanks !
Accelerometers respond to forces applied to the accelerometer body (the IC framework), whereas gravity accelerates all components of the accelerometer equally. When sitting on a table, the accelerometer reacts to the force of the table pushing up, preventing the fall. Hence it registers +1 g in the upward direction.

Note that accelerometers report zero acceleration when in free fall.
Thank you for your prompt answer. Another question if I may.

I want to apply a kalman filter to get the quaternion from these data. However, the kalman filter I am applying is for a right handed coordinate system where the Z directing downwards, unlike the system here. So i thought all I should do is to flip the Z axis (which I did ) .. however, I do not get right results when I move the sensor ? any ideas ? thanks a lot !