#define max(a, b)               (((a) > (b))? (a): (b))
#define min(a, b)               (((a) < (b))? (a): (b))

Zone    SensorIndex   Comment
  1           0       Zone 1 is the direct zone of sensor 0
  2           0       Zone 2 is the interpolated zone of sensors 0 and 1
  3           1       Zone 3 is the direct zone of sensor 1
  4           1       Zone 4 is the interpolated zone of sensors 1 and 2
  5           2       Zone 5 is the direct zone of sensor 2
  6           2       Zone 6 is the interpolated zone of sensors 2 and 3
  7           3       Zone 7 is the direct zone of sensor 3
  8           3       Zone 8 is the interpolated zone of sensors 3 and 4
  9           4       Zone 9 is the direct zone of sensor 4
        //
        // idx < 4 is to make sure it is one of the first four sensors (0-3) because we are going to
        // examine sensor idx and idx + 1 to calculate the interpolated strength between them.
        // So if idx is within 3 and idx + 1 is within 4 and both of the sensors idx and idx + 1
        // read non-zero IR strength, we can use the strength of the two adjacent sensors to interpolate
        // whether the IR beacon is closer to sensor idx or sensor idx + 1.
        //
        if ((idx < 4) && (acS[idx] != 0) && (acS[idx + 1] != 0))
        {
            currDir += (float)(acS[idx + 1] - acS[idx])/
                          max(acS[idx], acS[idx + 1]);