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Acc data explained

Please see below for a description regarding the accelerometer values

  • Unit

The unit of the Acc is 1/512 g. for example if we read a value of 1024 on one axis, it means we have 2g acceleration on that axis.

  • Acc X/Y/Z

we have 3 axes accelerometer data: acc_x, acc_y and acc_z. each axis is scaled to be between -8g to 8g. each variable acc_x, acc_y and acc_z is a 16 bit integer ranging between -32,768 to 32,767.

what I do is the following calculation:

(1) d_accX = acc_x[i]- acc_x[i-1]; d_accY = acc_y[i]- acc_y[i-1]; d_accZ = acc_z[i]- acc_z[i-1];

(2) Norm_of_d_acc = sqrt(d_accX d_accX + d_accY d_accY + d_accZ * d_accZ);

in phase (1) we calculate the difference in the acceleration in each axes, and phase (2) we get the norm of the vector of the difference in the accelerations. So basically the Norm_of_d_acc indicates movements. if the bracelet is physically fixed this norm gets towards zero and if it is in intense movements this metric shows a big value.