jQuery draggable plugin i want to update px to mm on drag event

jQuery draggable plugin i want to update px to mm on drag event

i want to know if there is any trick or hack to j-query Drag-able plugin,
so that on-drag event i want to update left and top position with unit mm
not PX for example
<div id="text" style="position:relative;top:22px;left:100px;">sample
text</div>
should change to
<div id="text" style="position:relative;top:22mm;left:100mm;">sample
text</div>
or how can i make a custom j-query plugin??to get this work