such a formula can be calculated quite well with an Arduino.
float x1 = ((((((7.716 * z - 37.57) * z + 73.23) * z - 71.39) * z + 34.81) * z - 6.785) * z - 0.001332) * z - 1.96e-008
This trick brings it down to 14 "simple" float operations instead of using power
Main problem might be that the Arduino only supports 32bit IEEE754 floats with ~7 significant digits.