Need to read a single value from text file to speedometer - html

Question

I have with me the canvas speedometer zip file. My intent is to read, from a text file a single number, and accordingly move the needle on the canvas speedometer as per the number read.
I have tried a few things and all I have managed to do is clunk up things a bit further. Any simple way to get around this, please? Preferably, editing the speedometer.html file such and adding a single button that reads the number from the text file and populates it in the text area provided on the speedometer web page?
Please help.
Edit 1: My bad. I should have included the piece of code I fidgeted around with for a brief while. Here goes the javascript snippet:
function func1()
{
var fileToLoad = document.getElementById("fileToLoad").files[0];
var fileReader = new FileReader();
fileReader.onload = function(fileLoadedEvent)
{
var textFromFileLoaded = fileLoadedEvent.target.result;
document.getElementById("maxvalue").value = textFromFileLoaded;
};
fileReader.readAsText(fileToLoad, "UTF-8");
}
And here's the bit about the 'Extract Value' button:
<input type="file" id="fileToLoad">
<button onclick="func1()">Extract Value</button>
The issue is I am getting sort of a clunky page. One which has a choose file button, and the 'Extract Value' button. And then, there are the begin and start buttons defined in the canvas speedometer API. All I am asking is this: is there a way by which I can have a single button on the page on clicking which the data (a single number) present in the text file gets populated on the ext field in the speedometer web page. This is all I want.
And in case anybody is wondering what the speedometer thingy is, please look here:
{http://www.uibox.in/item/68}
Apologies again for leaving a clearly vague question.