title: How do I fix 'nan'
body: <p>I am not sure why this is returning nan and what to do.</p>
  <pre><code>    g = accelerometer.get_z()
      G = (6.67*10)**-11
      m = (5.972*10)**24
      c = 299792458
      r = 38.5*(5.972*10)**24/ g* G
      deltatgprime = 5 * math.sqrt(1 - (2 * G * m / r * c**2))
      display.scroll(deltatgprime)
  </code></pre>