HTML5 Canvas Mouse coordinates

I am in one .html create two first canvas have mouseDown, mouseUp, mouseMove event's and I am need for second set mouseClick event, but...
I am don't get real coordinates. something like my second canvas is 400x400 pixels and I set code:

http://pastebin.com/xxvvRFat

secondCanvas.addEventListener('click', function(e) {
     console.log(e.pageX)
 }, false);
 

if I click on top left point mouse I am get in console 500~ number, but not zero...

Sorry for my bad English language

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