// HP = (Torque * RPM Weight) / 5252
var horsepower_calc = function() {
    var torque = Number(document.horsepower.Torque.value);
    var rpm = Number(document.horsepower.RPM.value);
    var horsepower = ( torque * rpm) / 5252;
    document.horsepower.HP.value = Math.round(horsepower);
    return horsepower;
};