jQuery计算日期时间差和同步

如图片一样 计算俩个日期之间的时间差
并且更改开始时间或截止时间是下方的阴历开始跟截止同样改变，改变成同一天
大神帮帮小弟 最好带注释 感谢了

 <div class="maincontent">
                        <h2>在线日期计算</h2>
                            <script>//显示当前日期时间
                                setInterval("jnkc.innerHTML=new Date().toLocaleString()+'星期'+'日一二三四五六'.charAt(new Date().getDay());",1000);
                            </script>
                            <div id="t1">
                                <p class="today">今天是</p><label id="jnkc" ></label> 
                                <div class="sj" ><span class="qz">起止</span><span class="jz">截止</span></div>
                                <form name="reg_testdate" method="post" class="date">
                                   <select name="YYYY" onChange="YYYYDD(this.value)"></select><span>年</span>
                                    <select name="MM" onChange="MMDD(this.value)"> </select><span>月</span>
                                    <select name="DD" ></select><span>日</span>
                                </form>
                                <form name="reg_testdate4" method="post" class="date4">
                                    <select name="YYYY4" onChange="YYYYDD4(this.value)"></select><span>年</span>
                                    <select name="MM4" onChange="MMDD4(this.value)"> </select><span>月</span>
                                    <select name="DD4" ></select><span>日</span>
                                </form>
                                <form name="reg_testdate1" method="post" class="date1">
                                   <select name="YYYY1" onChange="YYYYDD1(this.value)"></select><span>年</span>
                                    <select name="MM1" onChange="MMDD1(this.value)"> </select><span>月</span>
                                    <select name="DD1" ></select>
                                </form>
                               <form name="reg_testdate3" method="post" class="date3">
                                    <select name="YYYY3" onChange="YYYYDD3(this.value)"></select><span>年</span>
                                    <select name="MM3" onChange="MMDD3(this.value)"> </select><span>月</span>
                                    <select name="DD3" ></select>
                                </form>
                                <form name="reg_testdate2" id="jg" class="date2">
                                    <input type="text" class="tet" onChange="YYYYDD2(this.value)"/><span>年</span>
                                    <input type="text" class="tet" onChange="MMDD2(this.value)"/><span>月</span>
                                    <input type="text" class="tet"/><span>周</span>
                                    <input type="text" class="tet"/><span>日</span>
                                    <input type="text" class="tet"/><span>小时</span>
                                    <input type="text" class="tet"/><span>分钟</span>
                                    <input type="text" class="tet"/><span>秒</span>
                                </form>
                            </div>
           </div>