estimatedAccelerometerMa

Gets estimated accelerometer scale factors and cross coupling errors, or null if not available. This is the product of matrix Ta containing cross coupling errors and Ka containing scaling factors. So tat:

    Ma = [sx    mxy  mxz] = Ta*Ka
         [myx   sy   myz]
         [mzx   mzy  sz ]

Where:

    Ka = [sx 0   0 ]
         [0  sy  0 ]
         [0  0   sz]

and

    Ta = [1          -alphaXy    alphaXz ]
         [alphaYx    1           -alphaYz]
         [-alphaZx   alphaZy     1       ]

Hence:

    Ma = [sx    mxy  mxz] = Ta*Ka =  [sx             -sy * alphaXy   sz * alphaXz ]
         [myx   sy   myz]            [sx * alphaYx   sy              -sz * alphaYz]
         [mzx   mzy  sz ]            [-sx * alphaZx  sy * alphaZy    sz           ]

This instance allows any 3x3 matrix however, typically alphaYx, alphaZx and alphaZy are considered to be zero if the accelerometer z-axis is assumed to be the same as the body z-axis. When this is assumed, myx = mzx = mzy = 0 and the Ma matrix becomes upper diagonal:

    Ma = [sx    mxy  mxz]
         [0     sy   myz]
         [0     0    sz ]

Values of this matrix are unit-less.