MPU9250 Mag Sensitivity Adjustment (ASA)

Hi Everyone,

I am using Invensense's driver for MPU9250, the Mag inside MPU9250 is AK8963 , so in this discussion I am referring to the datasheet of AK8963 as well.

My concern is about sensitivity adjustment settings, which are programmed at manf. time. As per inv_mpu.c we are reading those adj. values and then adding 128 into it, but the datasheet of Ak8963 tells us to subtract 128 from the ASA values.

The formula is Hadj = H ((( ASA - 128) * 0.5 / 128) + 1)

So my question is are following this formula ?
How do you validate data from Mag ?