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https://ubuntu-mate.community/t/rpi3-and-i2c-spi/4541

The code normally ignores readings until an axis has been enabled.
The idea is to orient the IMU near the current extrema (+x, -x, +y, -y, +z, -z)
and then enable the axis, moving the IMU very gently around to find the
extreme value. Now disable the axis again so that the IMU can be inverted.
When the IMU has been inverted, enable the axis again and find the extreme
point. Disable the axis again and press the space bar to move to the next
axis and repeat. The software will display the current axis and enable state.
Available options are:
  e - enable the current axis.
  d - disable the current axis.
  space bar - move to the next axis (x then y then z then x etc.
  r - reset the current axis (if enabled).
  s - save the data once all 6 extrema have been collected.
  x - abort and discard the data.