jQuery mobile: Slider Widget

jQuery mobile: Slider Widget

I made a slider calculator with Jquery UI and then noticed it doesnt work
on touch devices, so I start over with Jquery Mobile.
For some reason I can update the value of the slider with the buttons, but
the slider itself won't move.
$("#plus1").on("mousedown", function () {
$('#slider-vertical').val(Number($('#slider-vertical').val())+25)
});
Please check: http://jsfiddle.net/MJ5WT/