var txtPercentagePreviousValue;
var totalValue;

function isNumberKey(evt)
{
    // copyright 1999 Idocs, Inc. http://www.idocs.com
    // Distribute this script freely but keep this notice in place
    /*var key;
    var keychar;

    key = (evt.which) ? evt.which : event.keyCode;
    
    keychar = String.fromCharCode(key);

    // control keys
    if ((key==null) || (key==0) || (key==8) || 
        (key==9) || (key==13) || (key==27) )
       return true;
       
    var regExp=/[0-9]/.test(keychar); 
    if (regExp == false){
		return false;
	}
	else{
		return true;
	}*/

    // numbers
    /*else if ((("0123456789").indexOf(keychar) > -1))
       return true;
       
    return false;*/

    var charCode = (evt.which) ? evt.which : event.keyCode
    if (charCode > 31 && (charCode < 48 || charCode > 57 && charCode < 96 || charCode > 105))
        return false;
    return true;
}

function setPercentagePreviousValue(txtPercentage, txtTotal)
{
    txtPercentagePreviousValue = document.getElementById(txtPercentage).value;
    if (txtPercentagePreviousValue == '')
    {
        txtPercentagePreviousValue = 0;
    }
    totalValue = document.getElementById(txtTotal).value;
    
}

function addProjectTotal(txtPercentage, txtTotal)
{
    var totalPercentageValue = document.getElementById(txtPercentage).value;
    var result;
    
    if (totalPercentageValue == '')
    {
        totalPercentageValue = 0;
    }

    result = parseInt(totalValue) - parseInt(txtPercentagePreviousValue) + parseInt(totalPercentageValue);
    
    document.getElementById(txtTotal).value = result;
    
    totalValue = result;
    txtPercentagePreviousValue = totalPercentageValue;
}