Here is another example that measures time. In contrast to the previous one where participants clicked into the image itself here we use submit buttons.
<HTML> <? $sec=explode(" ",microtime()); $sec=$sec[0]+$sec[1]; if (! $SEC) echo "<HEAD> <META HTTP-EQUIV=Refresh CONTENT=6;URL=$SCRIPT_NAME?SEC=$sec> </HEAD>"; echo "<BODY BGCOLOR=white> <FORM METHOD=POST ACTION=$SCRIPT_NAME>\n"; if (! $SEC) { echo "<CENTER><IMG SRC=123.gif></CENTER><BR> You have 6 seconds for the next question:<P> David Hume was born in? <INPUT TYPE=SUBMIT NAME=A VALUE=1711> <INPUT TYPE=SUBMIT NAME=A VALUE=1723> <INPUT TYPE=HIDDEN NAME=SEC VALUE=$sec>"; } else { $diff = $sec-$SEC; echo "Answering took you $diff seconds.<BR>"; switch ($A) { case 1711: echo "Correct. David Hume was born 7th May 1711.";break; case 1723: echo "Wrong. 1723 is the year when Adam Smith was baptised.";break; default: echo "You have been too slow..."; } } ?> </FORM> </BODY> </HTML>