Edit: Here's a JSfiddle
Edit2: The error is on this line: <input type="button" value="totalbandwidthresult" onclick="javascript:totalbandwidth();">  
Trying to have a button perform a calculation. The required variables are below, as well as the HTML where
I am getting an error onclick: Uncaught TypeError: object is not a function index.html:71
onclick
Here is my Javascript
function totalbandwidth() {  
    var fps=Number(document.calculator.fps.value);  
    var bitrate=Number(document.calculator.bitrate.value);  
    var numberofcameras = Number(document.calculator.numberofcameras.value); 
    var encoding = document.calculator.encoding.value; 
    if (encoding = "mjpeg")
    {
        storage = bitrate*fps;
    }
    else
    {
        storage = bitrate;
    }
    totalbandwidth = (numberofcameras * storage) / 1000;
    document.calculator.totalbandwidthresult.value = totalbandwidth;  
}  
The HTML:
<form name="calculator" class="formtable">  
<div class="formrow"><label for="rcname">RC Name</label> <input type="text" name="rcname"></div>  
<div class="formrow"><label for="fps">FPS</label> <input type="text" name="fps">  </div>  
<div class="formrow"><label for="bitrate">Bitrate</label> <input type="text" name="bitrate">  </div>  
<div class="formrow"><label for="numberofcameras">Number of Cameras</label> <input type="text" name="numberofcameras"> </div>   
<div class="formrow"><label for="encoding">Encoding</label> <select name="encoding" id="encodingoptions">
  <option value="h264">H.264</option>
  <option value="mjpeg">MJPEG</option>
  <option value="mpeg4">MPEG4</option>
</select></div>  
Total Storage: <input type="text" name="totalstorage">   
Total Bandwidth: <input type="text" name="totalbandwidth">   
<input type="button" value="totalbandwidthresult" onclick="javascript:totalbandwidth();">  
Basically - it seems that there may be something wrong with the syntax I used in the JS - but I'm not sure.