isdst.js

            //This is completely ridiculous.
            var jan = new Date(this.getFullYear(), 0, 1).getTimezoneOffset();
            var jul = new Date(this.getFullYear(), 6, 1).getTimezoneOffset();
            var today = new Date().getTimezoneOffset();

            if(jan == jul) {
                $('#daylight_savings').prop('checked', false);
            } else if(jan > jun) {
                //Northern hemisphere
                $('#daylight_savings').prop('checked', (jun==today));
            } else { //jun < jan
                //Southern hemisphere
                $('#daylight_savings').prop('checked', (jan==today));
            }