I tend to like inline statements.  Here is my new favorite.  I even commented!

protected int calculateData(byte[] data)
{
    // why the index++?
    // I want index 1 and 2, since i++ increments it after i been used
    // going int i = 1; Console.Write(i++ + "::" + i++); 
    // will "1::2"
    return ((index + 1) < data.Length) ? 

      calculateData(data[index++], data[index++]) : 0;
}

Update: Why I love it and why I did this
It is heavily compacted.  It is an inline if statement along with how I did incremented the index.  It won’t compile if you just ran it since I overloaded calculateData and have a (byte, byte) overload.

if index started at 1, it would leave as 3 from the function.  it calls calculateData like this, calculateData(1,2) and the next cycle would be calculateData(3,4).

So I use this function when I’m creating the ImuData return when I get data from the gyros and accelerometers.  I have a lot of data and the packets need to be parsed.  Since I know the order the items appear in when returning data, I just say, Battery = calculateData(data); in the proper order too.  I know the data will always be 2 bytes per variable too.  This is nice since I don’t have to worry about fixing indexes when I add / remove data from the IMU.

Thanks Alfred for calling me out on not explaining this.  I was in a rush and got side tracked.  Just like a teacher, always marking up my work.