<p>Test your Response time!</p>  
Click on "Start" first, and wait until the background color changes. As soon as it changes, hit "stop!"  

<script language="JavaScript">  
<!--  

//Reflext Tester- By Andy Scott (based on script by Jasper van Zandbeek)  
//http://www.geocities.com/SiliconValley/Station/4320/  
//Submitted to Dynamic Drive for inclusion  
//Visit http://www.dynamicdrive.com for this script  

var startTime=new Date();  
var endTime=new Date();  
var startPressed=false;  
var bgChangeStarted=false;  
var maxWait=20;  
var timerID;  

var colors=new Array("tomato","chocolate","limegreen","crimson","darkslategray",  
"aliceblue","mediumslateblue","cornflowerblue","darkorchid","darkkhaki"," coral",  
"darkolivegreen","cadetblue")  

if (document.all||document.getElementById)  
document.write('<div id="reflex" style="width:135px;height:135px;border:1px solid black" onClick="stopTest()"></div>')  

function startTest()  
{  
if (document.all)  
document.all.reflex.style.backgroundColor=colors[Math.floor(Math.random()*colors.length)];  
else if (document.getElementById)  
document.getElementById("reflex").style.backgroundColor=colors[Math.floor(Math.random()*colors.length)];  
else if (document.layers)  
document.reflexns.document.reflexns_sub.document.bgColor=colors[Math.floor(Math.random()*colors.length)];  
bgChangeStarted=true;  
startTime=new Date();  
}  

function remark(responseTime)  
{  
var responseString="";  
if (responseTime < 0.10)  
responseString="Well done!";  
if (responseTime >= 0.10 && responseTime < 0.20)  
responseString="Nice!";  
if (responseTime >=0.20 && responseTime < 0.30)  
responseString="Could be better...";  
if (responseTime >=0.30 && responseTime < 0.60)  
responseString="Keep practising!";  
if (responseTime >=0.60 && responseTime < 1)  
responseString="Have you been drinking?";  
if (responseTime >=1)  
responseString="Did you fall asleep?";  

return responseString;  
}  

function stopTest()  
{  
if(bgChangeStarted)  
{  
endTime=new Date();  
var responseTime=(endTime.getTime()-startTime.getTime())/1000;  
if (document.all)  
document.all.reflex.style.backgroundColor="white";  
else if (document.getElementById)  
document.getElementById("reflex").style.backgroundColor="white";  
else if (document.layers)  
document.reflexns.document.reflexns_sub.document.bgColor="white";  
alert("Your response time is: " + responseTime + " seconds " + "\n" + remark(responseTime));  
startPressed=false;  
bgChangeStarted=false;  
}  
else  
{  
if (!startPressed)  
{  
alert("press start first to start test");  
}  
else  
{  
clearTimeout(timerID);  
startPressed=false;  
alert("cheater! you pressed too early!");  
}  
}  
}  

var randMULTIPLIER=0x015a4e35;  
var randINCREMENT=1;  
var today=new Date();  
var randSeed=today.getSeconds();  
function randNumber()  
{  
randSeed = (randMULTIPLIER * randSeed + randINCREMENT) % (1 << 31);  
return((randSeed >> 15) & 0x7fff) / 32767;  
}  

function startit()  
{  
if(startPressed)  
{  
alert("Already started. Press stop to stop");  
return;  
}  
else  
{  
startPressed=true;  
timerID=setTimeout('startTest()', 6000*randNumber());  
}  
}  
// -->  
</script>  
<br>  

<ilayer id="reflexns" width=135; height=135;><layer id="reflexns_sub" width=135; height=135; left=0 top=0 bgColor=yellow></layer></ilayer>  

<form name="response">  

<input type="button" value=" start " onClick="startit()" style="font-weight:bold">  
<input type="button" value=" stop " onClick="stopTest()" style="font-weight:bold">  
</form>  

<p align="center"><font face="Arial" size="-2">Free DHTML scripts provided by<br>  
<a href="http://www.dynamicdrive.com">Dynamic Drive</a></font></p>