Combobox help

The following code isnt working for me, it works for the second but not the first. Any help will be much appreciated.

function gravestone_check1() {
        if (gravestonecb.getValue() == 1) {
            _global.gravestone1 = 1;
            _level0.gravestone1._visible = true;
            _level0.gravestone2._visible = false;
        } else {
             _global.gravestone1 = 0;
            _global.gravestone2 = 0;
            _level0.gravestone1._visible = false;
            _level0.gravestone2._visible = false;
        }
}

function gravestone_check2() {
        if (gravestonecb.getValue() == 2) {
            _global.gravestone2 = 1;
                    _level0.gravestone1._visible = false;
            _level0.gravestone2._visible = true;
        } else {
             _global.gravestone1 = 0;
            _global.gravestone2 = 0;
                    _level0.gravestone1._visible = false;
            _level0.gravestone2._visible = false;
        }
}

setInterval(gravestone_check1, 10);
setInterval(gravestone_check2, 10);

Thanks

Andy