When begin to edit a row, retrieve the editors and set the 'validType' on each field. Please refer to the code below:
$('#tt').edatagrid({
onBeginEdit: function(index,row){
var ed1 = $(this).datagrid('getEditor',{index:index,field:'listprice'});
var ed2 = $(this).datagrid('getEditor',{index:index,field:'unitcost'});
$(ed2.target).numberbox({
validType: {
greaterThan: [ed1.target]
}
})
}
});