var gos = 0;
function CalcBullRoof()
{
    var levelLength = parseFloat(document.getElementById("txtLevelLength").value);
    if (levelLength < 1000 || levelLength > 100000)
    {
        alert("Level Length must be between 1000 and 100000");
        document.getElementById("txtLevelLength").focus();
        return;
    }
    var curveRadius = parseFloat(document.getElementById("txtCurveRadius").value);
    if (curveRadius < 300 || curveRadius > 10000)
    {
        alert("Curve Radius must be between 300 and 10000");
        document.getElementById("txtCurveRadius").focus();
        return;
    }
    var roofAngle = parseFloat(document.getElementById("_txtRoofAngle").value);
    if (roofAngle < 5 || roofAngle > 40)
    {
        alert("Roof Angle must be between 5 and 40");
        document.getElementById("_txtRoofAngle").focus();
        return;
    }
    var endLength = parseFloat(document.getElementById("txtEndLength").value);
    if (endLength < 80 || endLength > 1000)
    {
        alert("Straight End must be between 80 and 1000");
        document.getElementById("txtEndLength").focus();
        return;
    }
    var arcAngle = 90 - roofAngle;
    var arcLength = (Math.PI * 2) * curveRadius * arcAngle / 360;
    var RAD = 180 / Math.PI;
    var setIn = curveRadius - (curveRadius * Math.cos(arcAngle / RAD));
    var topLength = (levelLength - setIn) / Math.cos(roofAngle / RAD);
    var totalSheetLength = topLength + arcLength + endLength;
    document.getElementById("spnResult").innerHTML = "Sheet Length = " + Math.round(totalSheetLength);
    if (gos < 2)
    {
        if (gos == 1)
            new Image().src = "http://www.blocklayer.com/Logger.ashx?p=BullRoof&a=BullRoof";
        gos++;
    }
}