Помогите разобрать JavaScript

Имеется следующий скрипт:
<script>
dig0 = new Image(); dig0.src = "image/dg0.gif";
dig1 = new Image(); dig1.src = "image/dg1.gif";
dig2 = new Image(); dig2.src = "image/dg2.gif";
dig3 = new Image(); dig3.src = "image/dg3.gif";
dig4 = new Image(); dig4.src = "image/dg4.gif";
dig5 = new Image(); dig5.src = "image/dg5.gif";
dig6 = new Image(); dig6.src = "image/dg6.gif";
dig7 = new Image(); dig7.src = "image/dg7.gif";
dig8 = new Image(); dig8.src = "image/dg8.gif";
dig9 = new Image(); dig9.src = "image/dg9.gif";

function clockTick()
{
var now = new Date()
var secunde = now.getSeconds()
var minute = now.getMinutes()
var hour = now.getHours()
if (hour < 10)
hour = "0" + hour
if (minute < 10)
minute = "0" + minute
if (secunde < 10)
secunde = "0" + secunde
now = null
minute += ""
hour += ""
secunde += ""
setjpg(hour.charAt(0),document.dg1);
setjpg(hour.charAt(1),document.dg2);
setjpg(minute.charAt(0),document.dg3);
setjpg(minute.charAt(1),document.dg4);
setjpg(secunde.charAt(0),document.dg5);
setjpg(secunde.charAt(1),document.dg6);
setTimeout("clockTick()", 1000);
}
function setjpg(num,docobj)
{
if (num=="0") docobj.src=dig0.src
if (num=="1") docobj.src=dig1.src
if (num=="2") docobj.src=dig2.src
if (num=="3") docobj.src=dig3.src
if (num=="4") docobj.src=dig4.src
if (num=="5") docobj.src=dig5.src
if (num=="6") docobj.src=dig6.src
if (num=="7") docobj.src=dig7.src
if (num=="8") docobj.src=dig8.src
if (num=="9") docobj.src=dig9.src
}
clockTick();

</script>

Вот собственно таблица с изображениями:

<table>
<TBODY>
<tr>
<td>
<img name="dg1" width="23" height="28"><img name="dg2" width="23" height="28">
<img src="image/dgc.gif" width="23" height="28"><img name="dg3" width="23" height="28">
<img name="dg4" width="23" height="28"><img src="image/dgp.gif" width="23" height="28">
<img name="dg5" width="23" height="28"><img name="dg6" width="23" height="28">
</td>
</tr>
</TBODY>
</table>

Не могу понять какой смысл несут следующие строки, объясните пожалуйста нерадивому студенту =)

minute += ""
hour += ""
secunde += ""